Changing unit for next level

I have a map where you have to get to the end of the path to begin the next level with out getting hit by player 11 (which kills you)
But what i wanna know is how do i change everyones level 1 units to the level 2 units while keeping collision detection (dieing when player 11 comes within some distance of unit)

You'll need variables for this. Just make a unit-variable array (an array is a variable that can hold multiple values, instead of just one as a regular variable can; the values in an array are distinguished by their number; this means that an array variable is a variable followed by a number) Then store into the variable the units of all players (each unit under it's own number, the number should be equal to player's number for easier future referencing). Then, when you change the level of units, just store the new units into the variable. That way, you can use the variable in your triggers on all levels.

adding a fireburn whit 100000 damage to all those units ?

new created units cant be used for unit whitin range triggers not even whit variables

Well, you could add new events...
Of course, doing it with a 1000dmg immolation would be a lot simpler, I at first went with a triggered solution because I thought there might be something more you could do with triggers, but nope, its all the same, with the "dying unit" and "killing unit" functions you can get the same values out as with the unit comes in range of unit triggers.