I've been told in an email from support that I can download version 4.1 as a free upgrade (I've only had 3.3 installed for 5 weeks) but every time I try, I am directed to the PayPal page for payment.

So how DO I upgrade without paying again?

if you have a paid version, you don't have to download it from the main site, but from your client area. The link you find in the my apps menu.

Thank you falcone - I was lookiong in the wrong place!