You are responsible for everything you believe, no matter how that beliefs were instilled in you. In the end, it came down to your acceptance of them.
Before you can change according to your will you have to stop and take stock about your beliefs. So for the start write down what you believe. For this I suggest you use a program like Excel or Calc instead of a book as you'll later come back to the list and add to it or edit it:
This list is the current state of your inner inventory. The deeper you gaze into it the more beliefs you will discover. In the future you can add new beliefs that you are forming.
Write your beliefs down as honest as you are able. Do not write down what you would like to believe or what you should believe.
Your existing reality is influenced by those core beliefs and not what you would like to believe.
When you have finished your list read it through again, see all you have written as thoughtforms that are stored in your consciousness and that are influencing the world you are experiencing in various degrees. Search for coherence between your beliefs and what you are experiencing.
Where does it come from
Now that you have a long list of beliefs you can start playing with them. Begin by adding a column labeled "Origin".
Examples for where a specific belief came from can range from parents, siblings, relatives, TV, radio, books, magazines, news papers, school, teachers, courses, religion, friends, experiences...
Even when you don't know where a certain belief came from examine it, sometimes it will dissolve by simple examination. Do try to pinpoint the origin accurately though.
Who thinks differently
This step now is an experimental shift in perspective. Pick a few beliefs from your list and ask yourself who believes differently. Examine where you discover resistance, this will be the area where you need to work more.
Do you want to believe that or not?
Again go over your list and add + and - (or something to your liking) to each belief. If you think a certain belief is positive or helpful, inspiring or motivating add a +, if you think it hinders you, or creates more problems than it solves add a -. If you feel uncertain add a / for example.
Now examine what you think will advance you and what hinders you (now something like Excel or Calc really comes in handy with filters).
Keep in mind though that negative beliefs are not necessarily hindering. It's non-acceptance and resistance that is.
Are you certain your beliefs are true?
Add another column to your list that you fill up with numbers from 1 (absolutely untrue) to 10 (hard truth). The numbers between range from "less true, but there is a possibility" over "I'm not really certain" to "quite true". Again be as truthful as possible, do not embellish anything.
When you are done it will raise the question what connection you discover between the strength of a belief and your experienced reality and the number you assigned to it. Usually it will be the beliefs that scored higher that affect your reality the most.
Now you add another column titled "Antipoles" and filter all the minues. Try to find an antipole for all those beliefs, ie that which you would like to belief or that which you think would further your cause.
When you are done you have a list of beliefs you will work with.
Earlier you added a column in which you judged your beliefs on their certainty or truth. Now start playing with them in terms of what would have to happen to raise the number to the next level. Obviously you filter all that are <10. Additionally you can think about what whould have to happen to make them less certain. Visualisation, affirmation, meditation, rituals etc are helpful there.
Start with the easier beliefs first so you get the hang of it then move to to the more important.
Add yet another column to your list in which you write all that you think supports the belief you hold, what evidence do you have, what experience makes it true for you.
Are those evidences also beliefs? If so, you have found some hidden beliefs that you can add to the list. The thoughtforms that support beliefs also have to be dealt with if you wish to change. Sometimes it's enough to find the connections to dissolve it all.
Translating experiences to beliefs
To find more hidden beliefs start a collection of experiences you have during your days. You will discover that there is a multitude of beliefs that originated in experiences and that you have automated. The positive ones can be quite helpful and effective, the negative ones however only enslave you.
Through the methods mentioned above you should now have collected a long list of your beliefs that you can work with, change, shatter, add to and experiment with.