First you'd have to define a variable called level for the object "Ship" and set to 1, because that's what you want the initial level to be I'd assume. Next, what I did was make a script called level up with the following code:
Ship.level = argument0
if Ship.level = 1
{self.hp = 2}
if Ship.level = 2
{self.hp = 3}
if Ship.level = 3
{self.hp = 4}
if Ship.level = 4
{self.hp = 5}
Now when you want the ship to level up, you call this script in the "Hp_Drawer" object and you set argument 0 to the desired ship level. The script will handle it from there.