without tearing the whole bike apart..
Hard to tell exactly how much that is but....
Suspension is usually an issue. You can replace the rear shock with several different models which would be an upgrade. Keep in mind that some people didn't mind raising the rear end so keep that in mind. There are quite a few threads here on that with info so search on it and then ask some questioins.
The front is a little more difficult. You can just change springs to a progressive kit when changing the fork oil and get better suspension or you can go the route of others and put a new front end on. That means tearing the front end apart. Besides better suspension, the fork legs are usually stronger with less flex and have dual discs for better braking. That's a rather large project that's fairly expensive.
Are your brake lines in good condition? You could consider changing to stainless and get a little better braking response.
If you don't have some kind of windscreen, then I would look into getting one of those soon. Look at photos and you'll see lots of choices.
Get your bike in good working order as BrianM recommends, ride it for a while and think about what would make riding better for you. Spend some time on here looking around. Take some pics and post 'em up.