How can I remove the skin discoloration above my upper lip?

Skin discoloration. You probably have a condition called melasma, which is sometimes associated with pregnancy and birth control pills. Regardless of the cause, there is no great way to treat this chronic problem. You might try a product containing hydroquinone which is modestly effective in causing the skin to become lighter. It may take months of therapy. Sunlight makes this worse, so use sunscreens.
Depends on the cause. There are many things that may cause discoloration of the skin. Several types of inflammatory conditions of the skin, allergic sun exposure, bacterial, viral or fungal infections, insect bites, friction, and cancer can all cause discoloration of the skin. Have it evaluated by a professional and get the appropriate treatment.