Exactly what you need to do is create an administrator account. You may think you already have one but that is only for certain actions.
To create one:
Click start, click all programmes, click accessories, right click command prompt and choose run as administrator, then click yes
then type in
net users administrator /active:yes
this will then be accepted
Log out of your pc, when you log on you will find a new administrator account. Log into that and you will find all the greyed out dimensions for custom sized paper all editable.
It is probably a good idea to create a password for this admin account so then go to the Control Panel to do this
