If the link is showing as underlined text, you can tap and hold. The pop-up menu will have an Edit Link options.
If the link is the fancy thumbnail version, you can tap and hold. In the pop-up menu choose View As, then Plain Link. From there you can use the previous method to edit the link.
Once done editing, you can once again tap and hold, then choose Show Link Preview.
Rather involved for the preview version of a link, but doable.