Or can I edit the one I have? Sorry, I'm new to this.

u can edit because if u buy a head texture u just buying a slot (i mean in TEXTURES) if u did buy the slot then just upload urs texture

^So simply, Yes, you can edit your texture whenever you want.

If you've bought a texture item, you can change the texture itself how many times you want... The item won't expire or something like that ^^

To change your, let's say head texture... Go:

Toroshop>Inventory>Textures> Scroll down to the one you bought and upload it...