Hi and welcome
Sorry to see you're leaving A2 ownership with your first post on here, but thanks for thinking to offer your A2 within our community first.
To upgrade your account to get Market access, click on your username in the black menu bar at the top of the page. Select Account Upgrades - there's only the one. As Erling says, there's a £2 fee via PayPal and you're done. (The PayPal is handled through our Shop software which may want you to register an account - the username/password for this can be the same as your main forum profile, or different - as you wish). Then you should see the Market section appear on the menu bar. Please note the
Market rules, especially those regarding having to state a price rather than just 'offers' (adding 'or near offer' is fine), and handling interests in the order that they were expressed. Interests should only be expressed on your advert thread rather than via PM, for the purpose of clarity for everyone concerned.
Good luck with the sale