As far as I know Adobe no longer offers standalone versions of Photoshop and you need to pay an annual fee to use it.

I just checked Adobe website:
Photoshop is available only through a Creative Cloud subscription that you pay for either monthly or annually. You can subscribe to Photoshop alone or choose a plan with multiple apps.

So I recommend you stay with the version you have. That is what I'm doing. Unless you are doing extremely advanced graphics such as 3D or video graphics, any older version will be fine. Photoshop rarely changes much through its versions; most releases have had superficial improvements that have no improvement for general use. Even version 5 is just as effective for most things as the most recent versions! So there is no need to upgrade.