I am completely remodeling my bathroom and the old toilet was ugly and wasted a lot of water, so I decided to replace it with a new water efficient model. Water efficient models maybe a little more expensive on up front costs, but the long term saving for the planet and your water bill are worth it.
Step 1: What You Need...
A toilet with any nuts, bolts, etc. that come with it
A wax toilet seal (It's round, made of wax, and is usually easy to find in the plumbing section of any store that also sells toilets)
A crescent wrench
A toilet seat/lid (if your toilet doesn't come with one. Toilets usually have very standard sizes, just remember to check what type of bowl your new toilet has)