It would be better to resolve the 'lagging and crashing' before upgrading the OS. Upgrading the OS as a first step is usually not the solution.
How about if you do two things. 1 - describe the problems in more detail and 2 - download & run Etrecheck and post a copy of the report here. It's a free diagnostic utility written by one of the members of the Apple Communities and is very helpful in diagnosing system problems. It does not expose any personal information, it just provides details about your system. Use the "additional text" button at the bottom of your reply to paste the report into your reply.