On the Delta Sport 2M it can be a little difficult if the original set-up is set hard.
Try to change the “angle of attack” (attach the flying line to another hole in the keel) and see if there is any change in flight behaviour. Also, when you take the Delta out of it's packaging for the first time, the rods inside the “leading edge” are moved upwards for packaging reasons. Push the rods down into their holding mechanisms.
The Delta Sport is not designed to be used with a tail, you can, of course attach a tail if you find it more aesthetically pleasing.