Issue with air flow in ducts

I figured this would be the best place to ask this one...

I have a vent, at the end of a run in which the airflow coming out of the vent is very minimal. The home is on a slab, so the ducts run through the attic of the home.

Other than trying to tweak the dampers, are there any other easier fixes to get more airflow to the last vent in the run? The furnace is an electric unit if that helps at all.

If there's no easier fixes, can someone advise me what options I should consider? I have been told that if I increase the duct size that branches to this point that I would get better air flow... is this true?

thanks again for the great advise!