The 4*40 is in essence a low wing trainer. In stock condition, it doesn't have much of a roll rate. As has been mentioned, you can clip the wings, install wider ailerons and seal the ailerons.

With one rib clipped from each side, the plane will roll faster and you won't notice any difference in landing.

With 2 ribs clipped, the plane will roll like a bandit, but will land a little faster, not like a scale plane, but you'll notice it coming down slightly faster. A buddy of mine has one with 2 ribs clipped and he loves the rolls.

Widen the ailerons. You can buy 2" aileron stock. I always also get balsa 1/4" tri stock to glue to the leading edge of the aileron stock. This makes it easier to hinge, saves carving and adds a little to the width.

Always on every plane, seal the aileron-wing gap. I use 3M clear tape. You can't built the wings close enough to keep air from seeping through. If you think you can, move down to the gulf coast with me and go through a hurricane. 75 mph wind will get through-trust me on this.

One final thing you can do is to add end plates. These will be great on the 2 clipped rib version. They will increase the roll rate and will lower the stall & landing speeds. Make them 3/4 inch wider than the rib outline. Lite ply works. You can get fancier, but I haven't noticed any difference.