Storage Space

Here are your options. You can delete some files to clear up storage space. Or you can purchase an external disk and then transfer files on to it so they can be erased from your HD to clear up space. Some computers can have their internal disk replaced with a larger one, but I wouldn't go there. External drives are now cost effective, compact, very easy to install with vendor provided USB cables and most do not require any external power. All you might have to do is to reformat the disk. That is the fast, easy solution I would recommend.

Please provide more detail.

Are you looking to clean up your iMac's internal storage to free space, or are you inquiring on external storage?

What year/model iMac do you have?