Sadly, genetics determine the shape and insertion of your muscles. You can make the muscles bigger by proper weight training but you can't change the shape of your muscles. That's genetics.
Someone who is 5'0 can't do anything to make his legs longer. He can make his legs bigger and more muscular, but the shape and structure of the legs are determined by his genetics.
The only thing you can really do is increase your bicep size. Developing larger biceps will make the tendons larger and fill out your arms. Your arms will look wider and fuller.
There are two bicep heads in your bicep. The long bicep head is the outer bicep head and the short bicep head is the inner bicep head (the head that is closest to your chest). Both biceps heads are used to contract the biceps whenever you do a bicep exercise but you can prioritize which bicep head does the majority of the work by changing your grip width.
A wide grip (wider then shoulder width) prioritizes the inner (short) bicep heap.
A narrow grip (narrower then shoulder width) privatizes the outer (long) bicep head.
Try training biceps twice per week. Add in 2-3 exercises for biceps after your back workout and then later in the week perform an arm workout where you superset biceps and triceps.