Is this your bike:
Walmart Roadmaster Granite Peak
All those items are adjustable!
The saddle tilt and fore-aft position can be adjusted by loosening the two nuts (one on each side) right underneath the saddle: Loosen both nuts; wiggle the saddle around; and retighten the nuts evenly.
The handlebar height can be adjusted by loosening the (usually) Allen head bolt that is accessed from the top of the steerer. Loosen the bolt just a little; if it is now sticking up, bash it with a hammer so that it drops back down; now adjust the handlebar height; and finally tighten the bolt.