I am not sure that just adding more frames would help much. There are some things you want to fix before trying to add more frames.
The front leg appears to be out of sync. When people walk, they tend to alternate leg with opposite arm. I might help to match forward and backward points of the front leg with back arm.
The nearest arm swings back and forth but the rest move to the end point before teleporting back to the start.
The legs are always behind the person. Try bringing the legs slightly forward forward at the farthest point further.
The arms look like they stretch a lot. If you focus on the person's joints and distance between the joints you might get better arms.
The one frame with the back arm behind the person looks weird.
Something like this uses the same images you posted just copy and pasted to get arms and legs moving together.
Overall the animation could use some work but, if you keep working on the animation, it will improve.
