Can someone please help me? I have downloaded Guitar Pro 5, but whenever I click on a song in the Ultimate Guitar archive that is tabbed in GP I am directed to a demo of another song with no option to download the track I originally clicked on.
That demo is for Tab Pro. If you scroll down below the demo, you will see a grey button that allows you to download.

For example:
Enter Sandman by Metallica - http://tabs.ultimate-guitar.com/m/metallica/enter_sandman_guitar_pro.htm

On the right hand side towards the bottom is a grey button with red writing that says "Download 'Enter Sandman' Guitarpro tab".