copy from one flash drive to another

Hope this is the right forum. If not, please redirect me.

I have an IMac and the latest Yosemite OS.

I have 2 SanDisk Cruzer flash drives. Each has thousands of songs on it.

I will call them flashdrive A and flashdrive B.

I want to do 2 things:

1) delete all the songs on flashdrive A.

2) copy all the songs from flashdrive B onto flashdrive A.

I do not want to delete any of the songs on flashdrive B, just copy them to

flashdrive A.