Not hard, unscrew some bolts, take the back tank off, lean the toilet over, replace wax ring, put toilet back, redo caulk, redo bolts, done. This is harder if you don't have a water shutoff right at the toilet though.
Yeah, what he said. You can do this, there are just a couple things to remember:
1. turn the water off at the toilet if there is a shutoff there. Often, older shut off valves will start dripping when you touch them. Put a container to collect it while you work and check if for a few days when you're done hooking it back up and turn it on. It'll drip a day or two before fixing itself.
2. if you don't have a shutoff valve at the toilet, turn off the whole house and have a couple bath towels to wrap there to collect the bits of water that come out.
3. Make sure to scrape out all the old wax, both from the part in the floor and the bottom of the toilet. Somewhere in there there is almost certainly a rubber gasket, that has to come out, too. If it's from the 60s or earlier, there may not be a rubber gasket, just wax.
4. when reinstalling, don't over-tighten the nuts. Keep two things in mind: a. this has to hold your fat ass, so it needs to be tight, and b. It's made of porcelain and you can crush it. Tighten it until you think it is good, then see if you can make it twist a bit with strong pushes from your knee. If you can, go tighter.
That's all there is to it. As you said it's tiled, I'd get the thicker wax ring. You should feel some resistance as you push the toilet down into it. It should be a little work pushing to get it seated back down into place.