Can I Upgrade from the Standard Version to Ultimate?

Hey all,

looking to buy the ultimate version of the game, but I'm a little tight on money with payments for a few things so I'm trying to balance it out, buy the $60 standard now and in a few weeks get the remaining $30 for the upgrade.

I just want to ask if such a thing is possible? Obviously if it is I expect you can only upgrade before the full game releases.

edit: u/supreme_Aimbot gave me $30 to cover ultimate. there are truly some great people in the world :)