Depends on the cause.
You could close down some of the programmes presently running that you don't need. This is what your warning has suggested. Fewer things running means a lower demand for memory.
You could check out how much memory your PC can have maximum, and how much it presently has, and consider a memory upgrade/addition. Riht clicking on 'my pc' and choosing properties can give a clue.
You could increase the size of your virtual memory. But that takes a bit of explaining.
You could check out the amount of free space you have on your C: drive. That can cause issues if the disk is nearly full.