How to Easily Change an Inner Tube on Your Mountain Bike: A Beginner’s Guide
First, remove the wheel from the bike by loosening the quick-release or removing the nuts. Then, use a tire lever to pry one side of the tire off the rim and pull out the old inner tube. Install the new tube, making sure it is not twisted or pinched, and then put the tire back on the rim. Inflate the tube to the proper pressure and reattach the wheel to the bike.