bike fit

Question
Hello

Have a small size mountain bike 17" that bought years ago from bike store. I think I should have had medium - 18".  I like the bike but only now I discovered that it may be slightly too small for me.  If I raise the seat so that my legs are almost fully extended, than I am too high from the ground.  Can ride like this maybe on asphalt but not on a trail.  On the trail, I thing that my legs are too bent.  I am 5, 10" inseam is 31".  Is there any corrections/parts etc. that I can make?  

Thank you,     Gabe

Answer
I'm not too up on sizing of mountain bikes. But generally they are sized smaller and shouldn't necessarily allow full extension.

But there is really very little you can do to retrofit such a bike. I would see if there is a mountain bike club in your area who can suggest something.

Scott<>