You could using SSMS

a). In design mode drop the column cID

b). Save the table

c). Go back into design mode insert a new column named cID

d). Set the column data type to int, do not allow NULLS

e). In the lower frame (column properties) expand "Identity specification" and then set (Is identity) to Yes and input values for "Identity increment" and "identity seed"

f). Close and save the table design window.

This should do it.