I see your problem, this shouldn't be too hard to fix.
Firstly, open the sprite for your character.
Then where you see the thing that says "bounding box", it should be set to automatic. Click manual and adjust the values. Set the bottom to about 8 pixels higher and test. Try different values until you find one that works.
Hope I helped,
There's no such thing as Bounding box? Only "Collsion Checking", "Name", Loading sprite/save/edit, Origin.
EDIT: Oh, You have to click "Modify Mask". Thanks for the hel pbuddy!