Adjusting a Shimano front and rear deraillieur

where the cable enters your derailleur, there is a barrel adjuster. Give it about a quarter turn clockwise and go for a test ride.

There are also adjusters on the shifters that will accomplish the same thing, but I don't feel comfortable giving clockwise vs counterclockwise directions on those.

 

there are tutorials all over the net. I googled and this popped up first

http://bicycletutor.com/adjust-rear-derailleur/

You can see the barrel adjuster in this picture

 

Generally, no, but you might. High and low should be adjusted once when the bike was built and then adjusted if you are having issues at the high and low gears.

The high and low screw set your limits, the problem you described sounds like a cable tension issue.

You should go check out the video sites, seeing is easier than reading what to do.

 

I think it was a Wally World purchase.

 

I would recommend breaking it in for a month, then bring it in to a bicycle shop and pay for a tuneup. (~$40-55)

 

Correct. When you bring it in, they'll adjust brakes, derailleurs, wheels, and check over the bike.