How can i improve mongoose 26 xr-75 dual men's mountain bike bicycle?

Answer 1

The recommended retail price and the spec list identifies this as really a low-end bike. You're starting from so low that there's really not much sense in spending any serious money on improving it.

Things that are borderline worth doing:

If you mostly ride roads you might try getting some smoother tires.

if the saddle isn't agreeing with you, you might try another one.

Some Kool-Stop (a brand) "Salmon"( a model) brake pads might improve braking.

Apart from small stuff like that, keep it lubed and adjusted and put any "upgrade" money aside for another bike instead.