In Nero burning Rom you can easily erase a RW disk in order to add new content by following this guide.
Take a look for the drop-down menus and configuration options:
1st Choose recorder Selects a recorder.
Use multiple recorders Erases multiple recorders.
2nd Select erase method to be used Selects an erase method. Two options are available:
Quick-erase rewritable disc: does not physically erase the disc fully, but only the references to the existing contents. The disc will appear to be empty even though the data is still physically available. Erasing a disc using this method takes between one and two minutes.
Full-erase rewritable disc: physically erases all data from the disc. The contents cannot be restored. Erasing the disc using this method takes longer than the other method depending on the type of disc involved.
Erase speed Selects the speed at which the disc is erased.
Erase Starts the erase process.
Cancel Cancels the action and closes the window.
Erasing a rewritable disc