There is an art to moving X days that is not found in most pilots. Try downloading some of the ALPA "Notepads" that deal with scheduling.

Generally speaking, you have to move whole groups of X days or move the last one or two X days in a group over to the next group. As someone else stated you can't create new groups of days off. Remember that moving X days comes after all the regular line holders have done trip drops and other reserve pilots have done PDs (personal drops). If there are lots of available reserve pilots, it might work. Good luck!