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cxwrench said it is not worth it. The bike as a whole is a disposable item not worth putting much time and money into. If you are looking to mountain bike there are plenty of excellent bikes out there designed for that purpose this bike was not in the least. Yes you will spend money to get a good mountain bike but I can assure you that money you spend if you spend enough and get the right bike will get you a bike worth owning a long time and riding a lot and even upgrading at points.
Look for something with an air fork rather than coil springs (generally) and find something with Shimano Deore and above or SRAM NX and above, look for hydraulic disc brakes and if you have the budget a dropper post is quite nice but don't try and cram too much into a tiny budget. The more you add to a bike the more expensive it becomes or the lower the quality becomes. Go to an actual bike shop, wally mart and similar box stores are not bike shops they have no mechanics and even if they assemble bikes on site that word assembly is used pretty loosely and they aren't looking over the bikes at point of sale or really at any point, they are churning them out quickly as they get paid by the bike in a lot of cases so taking your time and doing it right is just not part of the program. Even if they did the parts that come on it are disposable they aren't designed to work well or last they are designed to be as cheap as possible.
If you are really on a super tight budget find a local bike co-op and see if they have anything you can help restore or find someone maybe at your local shop who can help consult for money or food or beer or something and find an older bike that is in good shape.