Membership Premium Update 3.5.1.6 to 3.5.3.3

I want to upgrade my Membership Premium Plugin but I keep getting redirected to a 404 page. I've paid for the single monthly membership for the new membership plugin but it still doesn't allow me to upgrade. At the moment I just want to upgrade from 3.5.1.6 to 3.5.3.3 not to Membership Pro 2.