There is No Past
All that exists is in the present moment. Anything from the past is just a memory that remains in our consciousness. So, as far as the mind is concerned, every day is a new life. There is nothing physically stopping you from becoming a totally new person – the only thing in the way is the wiring of your brain.
Another thing I’ve noticed is that our sense of the past and who we have been is largely defined by our actions. So to redefine that past, all it takes are a few actions to confirm some new identity. For example, a few dedicated days of focused work can override the notion that you are a lazy person. Or a spontaneous social interaction can disprove the idea that you are shy. Of course, there is going to be friction the first few times you push back against this accumulated identity from the past. But if you keep pushing, who you want to become will eventually overwrite whoever you used to be.