XP collectibles and upgrading players

Please dont tell me its true that you can upgrade the overall of your current XP card players? I have all the 88XP players from season 3, like ekholm, fiala, stutzle, jones… So I could have actually used my XP collectibles to upgrade these players overall? Now i have just bunch of unusable 88’s that cant fit my roster. Ive seen people have like 92 Fiala so I’ve always wondered where did they get it.

So if it’s true that you can upgrade the overall, how and where? Thanks