upgrade 7.5.4 to plesk 8 : Problem

[netkom]

Hi,

I have a problem, i have a licence for plesk 7.5.4 and i have update to plesk 8 , the update is ok, but now my licence is not ok, i can't use panel control and i'm blocked, my question is how to return to plesk 7.5.4, because i'm blocked, it's not normal, i'm oblige to buy a licence for plesk 8 , swsoft must know how unistall correcly and go back to plesk 7.5.4

Thank's for your help, it's urgent

Frédéric