You can use the command dnvm uninstall. for example
dnvm uninstall 1.0.0-rc2-16343 -r coreclr -arch x64
You just need to change defaultto another dnx if you want to delete the current one. I described in response step by step how to install a new version of dnx, try it, and then uninstall it.
You will see that most of all dnvm uninstalldeletes the existing folder in %USERPROFILE%\.dnx\runtimes.
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