Give Minecraft more memory: Minecraft Launcher (official)

The official launcher sets memory per installation, as a Java argument.

1. Select Minecraft: Java Edition and open the Installations tab.
2. Hover over your NeoForge installation (the one that runs Dungeon Train), click ⋯, then Edit.
3. Click More Options, below the resolution fields.
4. In JVM Arguments, find the part that starts with -Xmx. It's usually -Xmx2G or -Xmx4G. Change it to -Xmx6G.
   • Only change that one part, and leave everything else in the box as it is.
   • Keep the - at the start and the G at the end.
   • If there's no -Xmx… at all, add -Xmx6G at the end, with a space before it.
5. Click Save.

Then fully close the game and press Play again. The new memory only applies from the next launch.

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Other launchers: see Give Minecraft more memory.