OTP bike are put together to make sure the component will last for a bit, obviously there are some OTP bike whose component doesn't (cheap MTB from Halfords), but generally it's fine.
If you find says, the handlebar feel a bit too 'close' to you, or too far out of reach, change the stem into a longer/shorter one to compensate, as well as choosing a saddle (can't exactly recommend you some as everyone arse is different), etc.
if you like how your bike fit you, how it ride, etc. then leave it alone.
OTP bike are put together to make sure the component will last for a bit, obviously there are some OTP bike whose component doesn't (cheap MTB from Halfords), but generally it's fine.
If you find says, the handlebar feel a bit too 'close' to you, or too far out of reach, change the stem into a longer/shorter one to compensate, as well as choosing a saddle (can't exactly recommend you some as everyone arse is different), etc.
if you like how your bike fit you, how it ride, etc. then leave it alone.