Well I am still playing a transmuter crafter character and i read up on constructing....constructs. And I came to the conclusion that you can do multiple types of upgrades:
a) Increase its HD as indicated. Some of the constructs have more detailed progressions described then others.
b) When calculating equipment that you want to attach to the construct, just use the crafting magical items rules (for the gold, XP cost and time needed).
c) For increasing size...well some have described progressions. Most of the constructs don't have this progression described, so just compare it with the ones that have.
a) Increase its HD as indicated. Some of the constructs have more detailed progressions described then others.
b) When calculating equipment that you want to attach to the construct, just use the crafting magical items rules (for the gold, XP cost and time needed).
c) For increasing size...well some have described progressions. Most of the constructs don't have this progression described, so just compare it with the ones that have.