Hello marymo,
If you want to remove Parallels 2.5 completely from the system, you may have to do it manually.
Here are the file list you may have to delete:
/Documents/Parallels/
/Library/Parallels/
MacHD/User/User account/Library/Parallels/
/Applications/Parallels/
And if you delete it, you will lose all the data associated with Parallels also.
Thank you.