OK, here's the thing. You won't get any options with a right click on your user defined parameters if those parameters are using dimension names that you have defined yourself.
So let's say you have a box with a length and width dimension called 'length' and 'width' and you have a parameter that says the height of your box is going to be length x width... You won't be able to delete that user parameter until you go into your relations window and rename 'length' to 'd1' and 'width' to 'd2' or something like that.
