Urska There are two ways to go:
1) change your subscription to Premium. You'll keep your current cards and add a Travel Card (up to three cards in total). You'll get all the banking services and all benefits of Premium at €5 or €7,99 per month.
2) Switch to the Travel Card subscription which only gets you the Travel Card and no banking services, just the card. This is free, but carries extra fees for withdrawals et cetera.
Switching from a promo or a premium to the Travel Card subscription makes no difference; you'll lose all benefits.
As said above: some perks come for free, but many don't.