Not a stupid question at all. In fact it’s more of a stupid implementation in Carrara. The way you’re supposed to do it according to the manual is to find the shader in the Sequencer under Master Shaders. Makes sense, right. Change a shader name in the sequencer, where you do animations. Absolutely ridiculous, and something that caused me anguish for a long time.
Anyway, when you find it in the sequencer you click on it, and on the right hand side of the interface a General tab will pop up, which shows you how many instances there are of it, and allows you to change the name with an editable box. You could also find it in the Shaders tab of the thingy on the right hand side (Properties panel), but in a scene of any size with a large number of shaders the update of that can be on the order of weeks, and it’s pretty useless.