You can Special Summon “Armed Dragon LV7” by using “Level Up!” on “Armed Dragon LV5”, because “Level Up!” lets you bypass the normal Summoning requirements.
Sending 1 Monster Card from your hand is a cost.
You can activate “Armed Dragon LV7”’s effect multiple times in the same turn.
You determine which monsters are destroyed by the effect of “Armed Dragon LV7” using the current ATK, not original ATK.