new life for a MacBook (2010)

My wife is the happy owner of a new (actually refurbished) MacBook Air. Nice birthday gift! 🙂 This replaces a white MacBook bought in 2010 which a while ago was given the name "Pokey" - because that is what it became.

I'm now looking to give this MacBook a second life as a machine that will mostly be used for Internet browsing plus a few other applications, but nothing taxing. I'm looking for some suggestions of how to go about that. I have not done any intensive investigation into what is causing the poor performance. It runs Mavericks, has the 2.4Ghz Intel Core 2 Duo, 4GB memory, 500GB ATA drive.

Any ideas on how to diagnose the problem and opinions as to whether I should just start all over with a new install (and which OS - it has Mavericks now) or if I might just be able to clean things up are all appreciated.

Thanks in advance!