While you work in iWeb, all hyperlinks can be active (on) or inactive (off).
By default, all hyperlinks are inactive, and you can edit them as you would any text. If you make all hyperlinks active (so that you can use them as you work in iWeb), you can still edit them.
Click near the hyperlink to select it (if you click the link itself, the target opens).
Use the arrow keys to move the insertion point into the hyperlink text, and then edit the text.