Many users refer to their hard disk as memory
Memory aka RAM is not the same as Hard Disk.
Your Hard Disk is like a filing cabinet and stores your data files, software, pictures, documents and music.
The Memory (RAM) is the area of your computer which is used as a working space by the processor to place files, data and software temporarily while it is working on them.
You need to make sure space is available in both these areas.
If you have more memory (RAM) on your computer, depending on how much your software needs your computer is likely to run faster, especially when your are doing many tasks at the same time.