Planning on buying mongoose snare (mountain bike)?

Full suspension at that price is not a good idea. The bike will be heavy to no real purpose, it won't perform well on or off road. At that price you might find a decent machine with front suspension only, But in order to manufacture that rear suspension, you have to make sacrifices, poorer components and materials. I also hope you are good at fixing bikes, Walmart does not service the bikes they sell, so you will have to be taking that bike in for service elsewhere. There is a reason why more expensive bikes cost more, they are built with higher quality components, lighter and longer lasting, wallmart has not found some secret formula for selling inexpensive bikes, all they are doing is making them cheaper, in both senses of the word. Upgrading to better parts would cost more than buying a better bike from the start, and no amount of tuning will make that bike work like a more expensive one. Your plan will cost more in the long run in maintenance and replacing parts than buying a good bike at the start