In order to sync your ammo and subscription from the old website into a new crate ("Crate 1") you need to update your payment method in the Profile. Once that is done the old site will sync with the new site within 10 minutes. You may need to log out and log back in but that usually isn't required.
DO NOT BUILD A NEW CRATE until you see Crate 1 - otherwise you may experience system issues.
To access your Crate Page, click on the Box Icon in the upper right corner of the screen:
If you are on a mobile device it might be under the "hamburger" menu. Like this:
Expands to this: