I have an ancient laptop so thats still pretty excellent, but I'm so tired of it and would like another before returning to school this fall.
Is it in some way to tell how much to sell? excellent ways to sell it? continue? I would be grateful if you have any advice! thanks!

Pretend you want to buy one & look at ebay & craigslist.
Have a look on ebay for best price.
An ancient one would go for about 500 bucks. Use E-bay