To tight a belly.

As for improve a body structure, and belly remove you must to analyze your meal, as hanging, clear belly is affects of over eating,and exercises will be effectively with a right ration, and these exercises doing in the normal body mass,and who needing strengthening for belly muscles,as for women's after  births, and training doing if doctor allowing.
Every exercise repeat till a light tiredness,initial breath is.
As doing on the morning exercises as at bed.
Lie on the spine, stretched legs, hands  under head, bend slowly legs in the knees and slowly return ti initial pose.

A same pose, bended left leg in the knee, rise head, and incline her to the front, return back, and same with an other leg.

Lie, legs bended in the knees,hands for the the body along, slowly straight legs up, same low theirs slowly, return back.

Lie, legs slight raised,hands for body along, turns with legs, like on bicycle.

As these exercises doing at home,work, or i the rest time.

Sit is on the chair edge, hands behind a chair sit, alternate bend legs in the knees and straight theirs.

Sit is on chair, hands are on the knees, alternately raise and low not bended legs.
And for hardening this exercise you must at the same time raise both legs.
Sit for chair s across, fixed legs, hands are behind head, slowly incline back, return back.

And slowly lead inclines to the horizontal and lower.
Sit is on the chair edge, hands behind and on the sit, rise legs under incline to imitate bicycle.
And to teach as to retract belly, and keep muscles in this position within a few sec, and doing this on an every free minutes, slowly rise a force for muscles of peritoneum press loading,that to strengthen theirs possibly.