please check if your using those parameters in ur report. remove those parameters from your report and then try to delete.

What sort of error message are you getting?

You need to make sure that the parameter is not just removed from the report itself, but from all references to it.  Check your Select Criteria, your Grouping, all of your formulas.  It's probably buried in there somewhere.

the parameter is not checked(so obviously not in use) i tried to delete and  even modify the parameter but nothing happen when i select these options. I only can change the parameter name.