Assuming you're referring to an HTML link, the process is actually quite simple. All you need to do is edit the anchor tag's href attribute.
For example, let's say you have a link that currently points to www.example.com. To change the link text (i.e. what is clickable), simply update the anchor tag's inner text:
Clickable Link
To rename the link, update the anchor tag's inner text:
New Link Name