I'm trying to activate the amelia license I've just purchased but the box for entering the purchase is greyed out.

I've deleted lite, uploaded the full version, activated, as per your guide.

I've done this over ftp and have command line access.  Is there anything else I need to delete before I can activate?

Disregard, fixed it.  The issue was when I installed lite I was under a different user than www-data, and so it was wordpress that couldn't delete amelia lite.  Went in and '  

chown -R www-data:www-data ameliabooking/

'

Then back to wordpress and deleted.  The reinstall of full was smooth.  

Feel free to close the ticket and post this in case anyone else encounters this.