I'm on invega (paliperidone) susstena and changing to Abilify due to weight gain, will I lose weight on abilify?

Can't predict. with any certainty. However, studies have shown that weight gain can in general be avoided with atypical antipsychotics when the patient is closely monitored with adequate exercise and healthy nutrition with moderate intake.
In vega weight gain. Maybe. Any drug can do anything. Have you seen a package insert?? I had 1 person gain 20lbs and 1 person lose 10lbs on Zyprexa (olanzapine). Watch your diet, exercise moderately and try the change following your prescribing professional's directions. Good luck!