Advice elsewhere said load WGT on a mobile and upgrade through this, one at a time - this didn't work for me.
What did work was:
I logged off WGT on my Ipad. Logged back in. Don't know if essential!
Tap on your icon to the screen that shows Equipment ; Apparel ; Stats etc.
Tap on Apparel (next to Equipment, NOT 'edit apparel')
This lists your equipped apparel. Tap on view stats (right hand side). In this screen it showed the amount required to upgrade. Upgrade as required.
Nb. This means you have to equip the apparel you want to upgrade first.
Hope this works for you.