Hello! If you mean how do you install a full tire spare or donut, then the video Dany suggest is great. If you're looking to replace the tire itself with a new one, you'll need to take it to a mechanic or a tire shop for the actual mounting and balancing since that requires pricy equipment that's not easily accessible to car owners.
Theoretically, you can follow the steps outlined in the video to remove the wheel/tire, install the spare, then take the wheel/tire to the mechanic to have a new tire installed and swap it when you get home with the new tire. However, that's likely going to be a headache and take a while for something that may not cost you much, if anything, for the mechanic to handle for you.