How do u change a bicycle rear 18 speed tire?

Im not even sure what size the wheel is. Its a huffy 18 speed mountain bicycle. Ive had it a good 12 years at least, and its still in good condition. I just wonder what size the wheel might be and how do i get the dang thing off especially with all the gears and such in the way. Any suggestions? Dumb answers will not get a nice response from me.

Idk if mine is just older or what, but it doesnt exactly say a size, it says how much tire pressure there is. But not a exact number like 26". I bought a 26 inch, but it looks like its too big. What other sizes might there be?

Right, to find out what size your tyre is, you will need to look on the side of your tyre. 26" is not an accurate description - there are many sizes that are labelled 26" in diameter. The full size will be something such as 26" x 1.75" (a common mountain bike size). It will be there - just look on both side of the tyre. As for removing the wheel, you only need to uncrew your rear wheel nuts. It helps to deflate your tyre first, which you will need to do anyway. Once you have unscrewed them, just pull the chain clear of the rear sprockets and you will be able to remove the wheel. Then - if you haven't already - deflate the tyre and remove it with tyre levers (I'm told you can use spoons if you don't have any). To replace it, just repeat the sequence in reverse. Remember to make sure that the inner tube does not get caught against the rim when you replace the tyre.

the tire has numbers on it.... mine is a 26"... so it says 26 on it...

as for getting it off, i'm not sure. i'm not very educated when it comes to bikes. but mine you can just unbolt both sides and slide it off kinda and then take the tire off the side without the chain and gears... but we have different bikes so i'm not too sure.

Edit:: well we have a few other bikes but they're all 20". just look everywhere on the tire. the number HAS to be on there somewhere lol

Look at the sidewall of the tire, it should show the size and the width such as 26" by 2.125". As for taking the wheel off just shift into the snallest cog in the rear (I think it is 6 for your bike) unbolt both sides, and slide the tire off.