I am currently a Knight Pledge. If i choose to do an "upgrade" - do i have to pay the full amount - or just the difference to the next upgrade? In addition, would i lose anything that is Unique to the old Knight Pledge that may not be available to the new pledge upgrade if i go through with it?
You can see the pledge page at https://www.pantheonmmo.com/join/upgrade/ and it will guide you through the upgrade process, including how much you'll have to pay in difference from one pledge to another. I'm pretty sure any upgrades from pledges you just simply pay the difference between the pledge values.
Kelenin is correct - you only have to pay the difference. As a refresher, here's what your current Knight's Pledge includes:
KNIGHT'S PLEDGE $100
2 Digital copies of the game
Alpha access
Beta access
Early name reservation
Additional character slot
Game Title: Pantheon Explorer
Stack of Minor Illusion Flasks
Explorer's Backpack
Tunic of the Ages
Keepsake Vanity Pet
Nothing from this pledge is transferred to your new pledge. So whatever is listed under the new pledge is exactly what you'll get.