Just blow some compressed air in from a can of air and blow it out. Just be careful not to blow too long at a time (to avoid condensation build up). I recommend short bursts of a few seconds at a time. If the can starts to feel really cold then take a break and allow it to heat up again. Just make sure that you start the blow out from the PCI bracket grill side and not from the fan side. Because you want to push as much dirt as possible out of the shroud. Once you see the dust subside then you start blowing a little on the radial fan.