First see it the condenser and evaporator fans are running.
If not you may be stuck in a defrost cycle.
I could not find a parts breakdown for this unit so cannot say where the defrost timer is. Usually in the control console in the fresh food section with a hole to let you rotate the timer cam or behind the kick plate at the bottom of the unit.
If you have no fans turn the defrost timer cam, if the unit fires up you need a new defrost timer.

If you have fans.
Check to see if the compressor is running, it should be warm and you should be able to hear it/feel it vibrating.

If it is not running you may have a thermostat problem or a compressor starter problem.

If it is running you may have a defrost problem.
Remove the evaporator coil cover.
If the coils are heavily iced/frosted over then you have a defrost problem.
If the frost patter is splotchy or just in one area you may be low on freon.

Here are a couple good sites with fridge repair/troubleshooting help.
Refrigerator Repair Guide: How To Fix a Refrigerator - ACME HOW TO.com
http://www.applianceaid.com/frig.html

We have been using 2 on the freezer settings. Will 4-6 make the freezer colder?

I am assuming that your unit is also a Kenmore/Sears.
Go to their parts website and search using your model number.

Then look in View Manuals and you should be able to download the manual.

Yes it is usually the higher the number the lower the temperature