Are you looking for ways to reduce the disk space used in your account without resorting to deleting websites or content? If you run WordPress there's a good chance it's not the blog itself that's taking up a lot of space, rather the media uploads. For image-heavy sites, this can quickly get out of hand because WordPress will not only store the full resolution image but also a handful of other small thumbnails so for each image upload you have at least 3 versions of the file (and in some cases more).
My favorite plugin for dealing with this is WP Smush. Install and activate the plugin and then you can have it cycle through all of your existing images and compress them without losing any quality. There is a good chance it could cut the size of your website in half without any noticeable difference. What's also great is that WP Smush works in the background for future uploads, compressing them at the time they're uploaded so it makes a great tool not just for cleanup but also ongoing background maintenance without any work on your part.
If you run a few larger WordPress installs and you're looking to free up disk space within your account this is a great option to lighten the load.