That really depends upon your budget! Some of the easiest make-overs involve painting the cabinet and updating the hardware on it. You can also get a newer shower curtain, soap-dish, toothbrush holder, rugs and towels!
You can change the fixtures such as the toilet and sink, change the wall, floor, and ceiling treatments and change the colors. You're only limited by your imagination.
Call a carpenter. Bathroom makeovers can be very tedious and difficult. You first have to pull out everything to reduce the floor and walls. Before redoing everything else.
