How to replace speedo cable on 65 4-speed

Hi all,

The speedometer needle on my 65 jumps around all over the place and doesn't go over about 30 mph. This cluter is out of a 66. I replaced the speedo with the original "long" 65 speedo. No luck, same deal. So, I have surmised that the cable must be the culprit. I know that I can get a new one for twenty bucks from any of the supply houses. I'm not sure, however, what is involved in changing the cable. The car is a 65 fastback A-code, 289 4-speed (toploader). Can anyone either give me tips on how to change the cable or maybe give me other leads to follow.

Thanks in advance, Richard