You need to be more clear on what you're asking and trying to accomplish.
Computer "memory" is also known as RAM, and is used while the computer is running to run programs and such. If you're getting "Out of memory" type messages? You need to clear out whatever's in startup and/or add more physical memory (RAM.) Most systems give 4-8 Gb RAM, with some at 16. (Higher amounts are atypical right now.)
This "clears" every time you shut down a program and/or the computer itself. It is not storage space.
If you need more *hard drive* space (space to store movies, install new programs, that sort of thing,) first I'd suggest uninstalling whatever you don't need. Did a bunch of garbage come with the computer, trial programs and things you never use? Go to control panel and find programs and features, then uninstall stuff you don't use. (If you don't know what it is, or it looks like a patch for something, leave it alone.) Then get something like CCleaner (free from priform, they'll try to sell you an advanced version, you don't need that) and run it to clear temp files and just generally clear what it can from the drive.
If you still need more room? There are two ways to go. Install a new hard drive (which may not be feasible on some systems) or get an external hard drive. While you *could* use a USB 3.0 hard drive to (potentially) run programs, I'd generally move data over to it first. (It'll also be useful as a backup.)
Without more detailed information on your computer and what you're trying to accomplish, it's hard to give more precise answers for what you can do.