HOW DO I ERASE MEMORY

More memory you get from a computer store ;)

Seriously...

A computer has 2 types of memory: main memory (RAM) and disk space

RAM is used by programs running. If you are out of RAM close some programs.

Disk is for storing files, pictures, videos, also programs and many other things.

If you want to find out what requires the most space on your disk there is a graphical disk usage analyzer in Ubuntu.

I believe it's found under "Accessories" --> "Disk usage analyzer" (I have no Ubuntu machine handy at this moment and can't check to be 100% sure)

Deleting files from the biggest folders displayed by the tool is the way to go.

Instead of deleting files you can of course also burn them to DVD

Hi :)

Yes "Memory" is usually used by techies to refer to Ram & "virtual memory" (=swap space). However most people could be talking about a variety of different things when they say "memory"

Swap space should be about 2xRam, any more than that is wasteful of hard-drive space and may even result in reduced performance. The Ram & swap work together to ensure the cpu gets the right data at the right speeds. There is a tiny amount of 'memory' on the cpu chips themselves but techies usually refer to this as "cache". Buying a new cpu is tricky and a lot of factors have to be taken into account. The main limiting factor is the cpu-socket type on the motherboard. Ram is a lot easier to buy as there are only 4 or so main types. Getting your swap partition to the right size is probably the easiest way to change the size of "memory" but that assumes we are using the techies definition of what memory is.

To see how much memory you have at the moment please give us the results of

free -m

This should show Ram along the top line and swap along the bottom so we can compare.
Good luck and regards from
Tom :)