Yes, you can change subscription types but as the fees differ, you must pay the balance* (pro-rata) by the end of your current subscription date. Once you do so using your chosen method of payment, you can then change your subscription immediately from "Entry" to "Standard".

* If you choose to pay this difference by credit card, the minimum possible payment is 70p / €1.00
* The play time from your currently paid subscription remains intact even if you change subscription type.
* FFXIV Coins are available as an additional payment method for Xbox Series X|S users. Please note that if you are only playing the Xbox Series X|S version, then the only payment method available will be FFXIV Coins.