Not really to adjust the overall length of the shock but there is a way to adjust the resting tension on the spring. There are two thin nuts on the shock that you can loosen. I believe on the picture of your rear shock they were on the bottom. you can loosen these to a point where it lowers the resting height of the bike. Just loosen the 1 not against the spring first then the other and make sure to tighten the two nuts against eachother when you find a good height.

These nuts have "teeth" on the sides and normally a special tool is needed. I usually use a dead blow hammer and an old screw driver which works as long as their not too tight.