Tiling an upstairs bathroom floor is similar to any other floor-tiling project, but is a little more complicated because of the tub and the toilet. The toilet has to be removed before you start, and you'll need a tile saw (instead of a standard score-and-snap tile cutter) to make the curved cuts around the toilet drain and the tub. Make sure the subfloor is solid and dry.
Turn off the water supply line to the toilet and disconnect it with an adjustable wrench. Flush the toilet to empty it of water. Remove the toilet by taking out the mounting bolts at the base and lifting the unit straight up. You will be left with just the toilet drain hole in the floor.
Divide the floor into four sections, using a chalk snap line to lay two intersecting lines over the area. Set the lines as if the tub isn't there. Use a carpenter's square to adjust the position of the second line as you snap it, to make sure it's 90 degrees off the first line.
Spread mortar over the lines, at the intersection, using a notched trowel, covering a few square feet. Set four floor tiles into the mortar, using the lines of the intersection as your guide. Put spacers between the tiles.
Spread more mortar and set more tiles, building out along the lines toward the walls. Lay all the full tiles that will fit. Let them set for a day.
Cut and lay the partial tiles along the walls and around the tub and toilet drain. Let the cut tiles set for a day. Remove all the spacers.
Apply grout to the tiles with a grout trowel, forcing it firmly between the tiles and squeezing it off the surface. Wipe up the excess grout with a dampened sponge.
Allow the grout to cure for 48 hours. Reinstall the toilet.
Wear eye protection when you cut the tiles.