Can i delete existing image sizes are regenerate using this plugin?

Hello,

you can disable not-needed image sizes with this plugin, but there is no button to delete old generated images.

There is a button, that allows you to delete old generated images only from this plugin, not from the default WP sizes.

But you can install any thumbnail regenerate plugin any they have this functionality, because they work with default WP image sizes, eg. this or this: