It is possible to use only 8 bits, but remember that your Vinput will be just divided by 255 levels because of the 8bit sample size.
Sampling will be done in 10bits but you can discard the two most significant bits. Remember that before you can go to 10 bits data, you must go through 0xFF hex or you must fill all the 8 bits first before data will fill the 9th bit.
Set bit 7 of ADCON1 (ADFM).
That makes the result left-justified. Then you just use the 8 bits in ADRESH and ignore the two LSB's that will not be stored in positions 7:6 of ADRESL.
This is equivalent to having an 8-bit A/D.
use the A/D converter as a 10bits sampler then dive your result by 4. It will remove the 2 LSB and bring your result as an 8bit integer. make sure when you first sample to use a long int variable.