You should've got rid of your high inhibition in your teenage years, but if you want to do it in your 20s, it's pretty simple, just start doing little things that give you a little shame in public, like:
- Go around with an unkempt hair/beard
- Go grocery shopping in light/gym shorts and an old t-shirt
- Not being polite
Well, i think you get it, so get creative. After some time, you will notice that, aside from a few exceptions, no one gives a flying fuck about you, and that you're basically invisible. After that realization, your high inhibitions will be lifted litte by little, untill that laid-back, not-giving-a-fuck attitude starts to seep into the social context, in a process that will make you low inhib by virtue of not giving a fuck.
In summary, try to be like "The Dude" from "The Big Lebowski" and eventually you'll be low inhib.