I can only assume you are doing this as a way to limit the number of bullets that can be shot?
Or do you have 5 bullet "icons" at bottom you are wanting to count down as player shoots?
If its the first one then use a variable Shots=5 and subtract 1 from it each time the player shoots and conditions out Shots=>0.
If its the second option then use a system picking event starting at the far left (X=0) and pick "furthers instance from X,0" then destroy and repeat each shot.
I would also suggest reading the Manual under "How Events work" and focus on the "Picking" of instances area... makes picking specific instances/copies much more understandable.