Reassigning IRQs

How the hell do I reassign IRQs of a device? It just won't work for me! What I do is I go into device manager (Start>>Settings>>Control Panel>>System>>Device Manager) then (in this particularly case I want to change the IRQ of my sound card) I click on sound, video and game controllers, then double click on my sound card. I go into resources, uncheck the Use Automatic Settings box, click on the IRQ Resource Type and press Change settings but I get this message. No modifications allowed - resource settings cannot be modified.