You are doing the normal one of mixing up memory and hard drive space.
Memory is temporary workspace for the computer to use while it is working, the memory in a computer is cleared evertime your turn your computer off
Hard drive space is where all your files and programs are stored, when the computer needs something, like a picture, because you have opened it to view it it is copied from the hard drive into the memory so the computer can work with it. stuff stored on the hard drive stays as it is even when you turn your computer off
Think of it like your hard drive is a storage cupboard and your memory is like a workbench, you get things out the storage cupboard and put them on the workbench when you want to use them and then put them back in the cupboard when you've finished to leave the workbench clear for the next thing you want to work on.
To find how much hard drive space you have open my computer and then your will see your hard drive listed with the drive letter C right click on this drive and select properties to see how much space is free.