How to tone arms without making them muscley?

I'm female, and started going to the gym about 5/6 months ago, 2/3 times a week. I go for general fitness and to lose weight, often going on a variety of machines, but I do not do weights. I do, however, often go on the rower. I want my arms to appear more toned but I don't want to do too much as I don't want muscley arms! What's the best thing I can do to achieve this?