Redmine

Hi all,
the issue is already asked and also, form what i read, is solved.
(http://www.redmine.org/boards/2/topics/2820)

But i'm not able to obtain the result executing any of the propesed solution.
How do i unistall a plugin and all the modification done to the database?
If i'm in the Redmine folder, what i've to type?!?!

Thanks for the help.