For a project of mine I need to use Kotlin 1.0.0-1038 (beta), but to install it I probably need to uninstall the newer version of kotlin, but it has no uninstall button where it should have.
How would I downgrade Kotlin? IntelliJ IDEA 15.0.4
IMPORTANT UPD: as @yole commented, this is a bad solution as it will break things. There is no proper way to downgrade a bundled plugin without breaking the installation. Instead, consider upgrading the project to the up-to-date Kotlin version.
You have the plugin bundled with IntelliJ IDEA. On your own risk, you can delete its folder manually from IntelliJ IDEA installation (plugins/kotlin subfolder). After that you will be able to install whatever compatible version of the plugin from zip distribution, but your IDEA installation will be broken (see the comment).
来源：https://stackoverflow.com/questions/35649488/how-to-downgrade-kotlin-in-intellij-15