I agree with Ginny. I think they're a lot easier to change if you're aware you have them to begin with and sometimes even when you recognise you must have them because you're not attracting what you want eg money it can be difficult to trace where that belief comes from. I know for some people recognising they have it can be enough to change it. For me, I prefer to think where has that come from, what led me to think that way consciously or unconsciously? and then find a way to change it.
If you can find where it comes from and generally it's a series of experiences that created attitudes about a topic whether that's money, relationships, work etc I've found the Morty Lefkoe info pretty useful in changing them. What he does is basically get you to look at those events again and say whilst it's understandable you made connections based on that experience at that time, are there alternatives ways of looking at it now that can lead to changes in thoughts in the long term.
Most events are just events it's us who add interpretation to them. Eg being offered a part time job is an event. If you've been unemployed for a long time that event might be interpreted as a wonderful positive thing. If you currently work full time and were hoping for a promotion being offered part time work might be interpreted as a negative. When similar things happen in relation to work etc, you may then begin to have limiting beliefs about your ability to earn money or compete in the work place. This might be viewed differently in retrospect.