Once resized images are cached in media/djmediatools/cache folder. When you change size of displayed images in component configuration or module parameters you have to purge images cache to force its recreation
It will not affect the original images.
To purge cached images click on "Delete x images" button
You also optimize images to increase page speed.
There is extra option to use CRON to optimize images. Just copy URL from CRON URL field and enter it as task URL in your cPanel.
Stylesheets are cached in media/djmediatools/css folder. You can purge the stylesheets cache to force its recreation what can be useful after update of DJ-Mediatools containing changes in album layouts dynamic stylesheets.