Walls and Ceilings - Closet to half bath, wall knockout

Ok, here is a wild question. I want to make a closet into a 1/2 bathroom. I need to eliminate the exsisting door and knock a small wall out in the hallway to make a new door. This thing is going to be tiny but at least a person can go to the can without going downstairs. The ceilings are high so I guess there would be plenty of room for a header. How do you tell if a wall is a load bearing wall???

What is above? Attic? Another level?

There is an attic that you have to grawl in.

Check the attic above the wall.

If you live in an area where building codes are enforced, permits are usually required for any changes to structures. Some may not require a permit for knocking out a non-loadbearing wall. The usual advice on load bearing walls, is to contact a structural engineer. Sometimes building contractors and inspectors can not accurately determine if a wall is loadbearing. Loadbearing walls often run perpendicular to floor or ceiling joists. Proceed with caution if wall runs parallel with joists, as these can conceal hidden support posts and columns.