Why does Internet Download manager occupy a lot of space on my C?
The way a download manager works is by allocating the space needed to download the whole entire file. It then creates a that file like a normal download would and as it downloads that file writes the data into the correct location. Depending on your download manger, if you remove a download it may keep that file in the temp folder, when you want to remove a download, look at the options and select remove file(s)