It is possible to simply right click on a folder and convert all the folder's audio files.
When you right click on a folder, you will see the option "Convert this folder's audio files to" and a submenu to select the destination format.
Optionally, you will be able to convert audio files in all sub-folders as well. This can be very useful for changing the file format of your entire music library! For example, you might like to free up some space on your computer and would like to convert all your 192 kbps MP3s into 128 kbps OGG files, for example.