With ImgBurn in Write Mode, there are two 2 ways to get to the erase disc function:
Go to Tools>Drive>Erase Disc>Quick or Full Erase [whichever you choose]
Click the icon with the little eraser over a disc that’s right below the drive selection box. (first screenshot).
–ImgBurn may force you to do a full erase to properly format the RW. [If you used ImgBurn exclusively to erase, it would only force you to do a full erase once, and you could do a quick erase any time after]. This can usually be changed by going to Tools>Settings>Write (a tab)>uncheck Prefer Properly Formatted +RW (second screenshot).