I have a DVD-RW disk that I want to erase but can't figure out how to do it. Would appreciate help. Thanks!

I'm running Snow Leopard (10.6.8) on an iMac. I have iDVD and DVD Player. The disk is a Memorex DVD+RW. I used it to transfer a program to another computer. Now I'd like to erase it and use it again but I can't figure out how to do that.

The disk info says that I can read only, but in the drop down permissions menu it says that I can both read and write. That in itself is confusing.

I would be very grateful for any assistance with this issue. I bought RW disks so I could reuse them; I'd hate to throw this one away.