What would be a good workout for me?

Im not doing this to lose wight i just want to gain bigger arms i have strong legs there pretty big but my upper body is pretty small my forearms are and my my biceps and triceps arnt to small but i want them bigger if you have a good but not hard routine for me to fallow i wuld be happy im only 13 and weight around 115pounds i really want to get bigger arms what would be a good routine for me please help and what can i eat to get the results faster im going to work out at home i have 15pds dumbells and thats it