Don't need any special apps to do this ... plug in your X to your computer as a USB connection (the option for USB Mass Storage Mode will appear on your pull-down notification bar above the home screen - check the appropriate box). Then open your X's SD card as if it were a flash drive.
There will be a list of folders and you can find music either as a separate folder or in the "Media" folder. You can delete right there or drag/drop any files onto or off the SD card. You can also create folders and organize any of them, even rename the folders (but don't change those for Media-related content) You can edit any of the folders on the Xs SD card in this manner. There is no need for specialized apps to do this.
BTW - don't install the Moto app/program that keeps wanting to install each time you hook up your X to the computer as a USB connection. It's essentially worthless. Just click cancel for any message that pops up. Annoying, but better than having it launch each time. If it's already installed on your computer, uninstall it.