Here is the IRS instructions. Please read it:
http://www.irs.gov/pub/irs-pdf/iw2w3.pdf 

Boxes 1 through 20. For the items you are changing, enter under “Previously reported” the amount reported on the original Form W-2 or on a prior Form W-2c. Enter under “Correct information” the correct amount.

Boxes 1 through 20. For the items you are changing, enter the value for both “Previously reported” and “Correct information”. If any item shows a change in the dollar amount and one of the amounts is zero, enter “-0-.” Do not leave the box blank.

Boxes 1 through 20. Do not make an entry in any of these boxes on Copy A unless you are making a change.

Thanks,

---

I need to correct W2 form box 10 only. Do I still need to enter all other information on form?