You just edit the last half of the link (the bit that repeats the initial link) between the first "]" and the last [/URL], starting with the http or https and replace that with whatever text you want to be shown. e.g.
http://www.buildyourownguitar.com.au...l=1#post137717
with some editing can become:
Link to Wazkelly's previous post

If you're not 100% clear, do a 'reply with quotes' on this then you should be able to see the code.