Plastic shims — inserted at certain locations — take up gaps between the base and the floor and provide a solid, secure foundation. Install the toilet over the toilet flange following the manufacturer's instructions. Rock the toilet side to side, front to back to determine where the gaps are located.
Place a new wax ring on the bottom of the toilet around the drain hole with the rounded side facing up. Set it back into position over the floor drain, making sure the holes in the toilet base slide over the flange bolts.
Hammer a shim gently between the floor and the toilet base to bring a low side up. Continue to check the level in several directions around the toilet bowl and add more shims as necessary to level the bowl. When the bubble is level in all directions then tighten the bolts down firmly.
In your case, you often just need a few simple tools to replace a toilet.. bond between any tile grout or caulk that should be between the toilet and the flooring.