Depends a bit on what model year it is. If it is a “Retina” machine, you won’t be able to upgrade the components in the machine except for the drive with some adapters. If you have a machine from 2012 or before which ich chunkier and has a DVD drive, you will be able to change the memory (RAM) and the hard disk. Software wise the machine is no longer supported by the newest OS, but with so called patchers you can run modern macOS versions on your laptop, as the other comment mentioned.