hi, i am pretty new to cycling with limited knowledge in the bicycles. The most confusing part is the BB, even I have googled it! Hope someone can let me know.

I need to change the crankset (from 175mm to 170mm). How can i tell if I have BB30 or GXP or whatever (how many types are out there?)

Does all road bike BB compatible with either type?

Please advise or direct to previously discussed thread. Thanks.