Learn more about this change here.
For help regarding Aternos, we recommend you to visit our support center.
You shouldn't, but in any case that's what backups are for. Additionally, if the button on a software/version says 'reinstall', it will reset your server with the new software/version, if it just says 'install', it will not reset your progress. Eitherway there will be a pop-up box that tells you prior to installing the new software/version when it will reset your server.
Thanks man! 
Had to ask cuz 1.18 changes world generation and it could affect my base.. thanks anyways!!
OK, First off, I'm sorry if this question makes me seem stupid, but i really had this doubt.
I have an SMP with my friends and it runs on Version 1.17.1 (I play on TLauncher) and I wanna update the version to 1.18.2. I just wanna confirm if i'm gonna end up losing my world progress cuz I have a huge underground base which took me a week and I don't wanna lose all that progress. Please do let me know what i can do.
Thank you in advance!!
