Okay, so we're going to talk about how to figure out if you have a cassette, or a freewheel on your back wheel, which is the gear cluster, and how to install them, and how to take them off.
So when you look at your wheel without any gears on it. The freewheel wheel basically just has a bunch of threads on it. And the actual freewheel has a whole gear cluster that has bearings and teeth inside of it with the threads on the back. So you want to make sure that you get the correct size freewheel. The amount of teeth on the bottom which is the high gear and the amount of teeth on the top which is the low gear.
So I'm just going to make sure it's the same as what you have now, or if you want to change it you can ask a bicycle mechanic or professional how you can change that.
So to install that you want to make sure that you put grease on the threads. You can put it on the inside of the freewheel, or you can put it on the actual threads of the wheel. And then you're going to thread it on so making sure that it's really, really nice and straight, and that's going on really easily.
If it feels kind of tough that usually means that it's cross threaded. So once it's all the way on, what you're going to want to do, is you're either want to put it on your bicycle and put the chain on, and then push down on the pedals so it get's nice and tight or you can use a chain whip. That's one of these things and basically you just wrap it around the freewheel. Righty tighty, lefty loosey. And then you're going to cinch down on the actual freewheel to make sure it's really tight on the threads.
Now to take off a freewheel there's a bunch of different tools. They all essentially do exactly the same thing, except they have different splines on them. so this is a Shimano one, it's the most common. And then there's ones that have two pins, four pins, some that have different types of ridges. There's all different kinds, so you may want to talk to a professional about which kind you have so you're not stripping it out.
Then you either use a wrench or a vise. A vise is a lot easier because you can get a lot more torque and then you're just doing righty tighty, lefty loosey. And the freewheel comes right off.