Move movieclip

I am trying to make the movieclip move to the right then when it gets to the end of the stage go back to the left. I tried different codes but still lost. here is the code I am using:
on (release) {
this._x = this._x+5;
if (this._x>=550){
} else (this._x =this._x-5);
}
I am trying to make it go 5 pixels on(release) and the back 5 pixels on(release)
when it gets to the edge of the stage.