8 bits is greater than 4 bits.... the reason for running it in 4-bit mode is to free up precious I/O pins...
I would take a long hard look at the data sheet for that device and then re-read it. setting up the ADC is not a hard task but it requires you to understand what and where with the PIC
All you should need to do is define and set up the pin for analoge input, Initialise the ADC and then read from the ADC.
There should be a help section or library within ur compiler this will have all the relevant information you need. I have not used AVR Studio and so i am not familiar with the function list.