How can I fix my Servis M76845-A Fridge Freezer?

I have a Servis M76845-A Fridge Freezer.I keep getting ice on the back of the fridge on one side and it freezers anything in the salad boxes or on the shelf above.Is it the thermostat or is it something else and is it worth repairing. If so can I do it or do I have to get someone out. Not sure how old it is. Sometimes get ice on bottom of fridge and there is some at the back at the bottom I noticed today. Fridge is only on 1 and the freezer seems to make ice cream rock solid.