You can click on Search present on taskbar or press Ctrl + Q. Search "Configure Java" and click on it. That should open the Java Control Panel. ... Sign up to request clarification or add additional context in comments. More on stackoverflow.com

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If you're on Windows 10, the OS is literally so garbage at file associations someone wrote a utility specifically to make Java open .jar (Java Archive) files. It's called Jarfix: https://johann.loefflmann.net/jarfix I recommend trying that. I've even tried manually finding the Java Runtime and selecting it to open Java files and it didn't work, but Jarfix got it. More on reddit.com

You have to assign the ram in the launcher. The instruction for that are here . More on reddit.com