Just take the inner fender liner - the plastic bits - loose from inside the wheel well.
You can do it alone - I have - but a helper would be handy.
Geez, it's been a long time ago, but as I recall you take the threaded collar off the antenna base and slide it out.
STOP HERE
Be sure you tape / tie / attach something to the cable so you don't loose it inside the wing!
Attach cable to new antenna - replace it the the fender - hold on to the inner bit and re-tighten the collar.
Ta-Daa!
...did I mention to be prepared to scrape up your forarm while jamming it between the metal and plastic fender bits???