I will also point out that if you can't rename a USB drive in Finder, then maybe it's because you can't write to it.
There may be several possible causes for this, such as the USB drive being in the Windows NTFS format.
Discover the format by selecting the USB drive in Finder, and doing ⌘I (Get Info). The format should appear near the top of the Get Info window, next to the label "Format:".
The format can also be discovered in Disk Utility. Select the named volume, and the Format: appears at the bottom part of the window.