Hi Coryn,
You should not use that lens while there is still sand stuck into it, it can severely damage the lens!
If you want to clean it yourself you have to take the lens apart which can be very tricky and potentially dangerous. Your best bet would probably be to take it to a repair shop and let them do it. You can also send it back to Canon themselves so they can repair it but be aware that this can take several weeks and might be expansive.