Choose Edit > Invert layer in the Canvas Layer Editor.
You can easily invert a mask so that masked regions become unmasked and unmasked regions become masked.
Edit > Invert layer does not affect Shape layers.
If you select an image layer then choose Edit > Invert Mask, all masks linked to that layer are inverted.
If you select an image layer then choose Edit > Invert invisibility mask, all invisibility masks linked to that layer are inverted.