Thanks for your reply mates!!
I finally uninstall tmnf Without unistalling personal documents and scores, etc....
I remember when installing TMU, it took all my account infos
and so when i login , all my fx,replays,mt-stuff,etc..was there.
so i did'nt needed to import or copy my stuff from trackmania/ documents to
tmu /documentssince the folder dosen't exist or have been create by the installation of tmu.
(the only folder created is "TrackMania United" that content "Config" folder.)I only copy/paste the files from TMunlimiter to TMU

as you said.
then at my 2 nd login ,i first hade to download 2 updates (to change to TMUF) from the Official site and then
i went on the account icon to change my serial number, and VOILA!
So in my case i uninstall TMNf with no problem from TMU tha is now TMUF
I have now in C:/PROGRAM
*Trackmania United
*TmUnitedForeverAnd much happier !
:gamer: