Presumably you have persistence file of over 1G any thing less fills up as the complete home directory that is made in the file. Any updates you've done will take up lots of room in the file; any progs you've installed also take up valuable room.
As distros become bigger so will the amount of room it requires to just make up the files required to be in the persistence file. The best way to use persistence is alongside a remastered iso with all the required programmes and all updates included in the iso. ( although this is generally beyond the new user most lightly to use a liveusb.)
You can mount the persistence file on an a live cd to retrieve the files (or an installed mint)
Open a terminal in your home folder then type
You'll only need to do this once as you’ve just made a folder (mkdir = make directory) called caspermnt in your home folder.
sudo mount -o loop casper-rw /home/XXXXX/caspermnt/
Your mounted casper-rw file will then appear as a drive icon on your desktop and a folder in home.
sudo umount ~/caspermnt/