Wont that get the dust all over the rest of my pc? There's a lot of it
Some may fall on there, yes. But then you just use more canned air to blow it off that and out of the case as best as you can. Only way to clean it fully would be to remove the components and clean them individually separate of each other to prevent the dust from collecting. You could also try adding some paper towel on the components to help collect the dust as it falls and settles.