Modifying the 'Sales Stage' Field

Hi all,

I'm trying to modify the Sales pipeline report, we do not use the 'Sales Stage' field, in fact it has been removed from the opportunities form altogether, but I can't find how to remove it from the actual Sales Pipeline report, so I thought if I can't remove it I'll modify it as 'Qualify, Develop, Propose and Close', are all pretty irrelevant to what we do, but when I go to edit the field, it won't let me..... Can anyone let me know if there is a way of removing it from the Sales Pipeline so I do not have a long list of items that say 'Not Specified' or if I can't remove it, a way of changing the list to one that is more relevant?

Many thanks