Here's a quick 4 step process in removing a valve core with a valve core tool (valve cap type).
Once the valve core tool is inside the valve, simply turn it counter-clockwise a dozen times until the core comes out. To replace the valve core simply pop it back in and turn the valve core tool clockwise until the valve core is hand tight! Easy.
And now you know!
However, if you're unsure or need help with all things pram tyre and tube related, please do get in touch, we're happy to help.