Goto `Tools` in Android Studio and Select `AVD Manager` and it'll display the list of virtual devices you have. Choose your emulator and in it's drop-down list press `Wipe the data` and run the app.
If the above doesn't work then Choose your emulator and in it's drop-down list press the Show on Disc button. It will take you to that hard drive, then just free up some space. Not sure about the minimum space.
Even try this also:
Click Tools -> AVD Manager -> Click on edit icon of the emulator you're using -> Click Show Advanced Settings -> Under Memory and Storage reduce the internal storage specify something like 2048MB for an emulator that comes with Google Play store or less for emulators without the Google Play Store.
**Note:** `Do not delete anything from avd folder !`

It's not about `RAM`, if you are beginner just use the recomended amount of `RAM` when creating new `AVD`. In order to solve your particular problem, Go to the disc where is stored your `AVD` files, mine is in this `Path`:
> E:\avd\.android\avd\Nexus_5X_API_27_1.avd
and free up some space on that hard drive. Do not delete anything from avd folder ! If you do not know on which hard drive is stored your AVD files, go to `Tools->AVD Manager` [![AVD Manager][1]][1] Choose your emulator and in it's drop-down list press the `Show on Disc` button. It will take you to that hard drive, then just free up some space. Not sure about minimum space, I have `20Gb` and it works perfectly, you can start from minimum 5Gb. Also in that drop-down list try to `Wipe the Data` first and run the app, before trying to do all mentioned above.

[1]: https://i.stack.imgur.com/df3Dm.png