As indicated already in our community, Miniclip strongly suggests upgrading any Guest account to avoid any data loss. Why?
Imagine that you finally managed to finish that customized skin you have been working on for the past few days and you are getting into the game.Then, one day, you lose your phone or uninstall the app…
Everything attached to it is recovered because you saved everything, but you forgot to link your game to Facebook or Google. Oh no, there goes all of your progress...
In situations like these, you will lose ALL the information (the level you are at, purchases, coins, DNA, skins items, etc) related to that account. And, in most of the cases, there is no way for us to recover your Guest Account, so it's lost forever.
Before anything like this happens, let's save that Agar.io account! How?
Go to your settings
Choose the login type you prefer: "Login with Facebook" (available on Android and iOS devices) OR “Sign in with Google Play” (available only in Android devices).
That's all it takes, now your account is linked to your Facebook or Google Play account and you won't lose it.
Very important: Make sure your Facebook or Google Play account was never used before in this game, or else this is not going to work.