lifeyy are they not already ‘skinnier’ ?:halo:
if by upper arm u mean the whole upper part which includes the bicep and tricep area of the arm, then as kali billi said, bicep curls and triceps pull down are effective… give it enough rest after ur workout.. and try not doing bicep and tricep exercises on the same day.. also, dont overtrain either. Last but not the least… pray!..ask Allah for proportional and skinner arms..u never know this might actually work.