How can I adjust the linkage on my 1992 Honda Prelude?

I have a 1992 Honda Prelude five speed and recently I lost third and fourth gear, but occasionally they will engage and my first and second gear will not work. This only happens when I hit a bump or something a long those lines. I was either wondering how to adjust it or how much it would cost to have someone professionally do it. I’m not sure if this question is out of Fluther’s boundaries but I figure it is worth a try.