install and update the rulesets in osu!lazer with rūrusetto.
Ruleset files can be obtained at rulesets status page and then clicking on the Download latest version on the desired ruleset.
The changelog and download link will automatically update when a ruleset is updated.
In osu!lazer’s setting panel, there is a button to Open osu! folder within the “General” section. On windows you could navigate to the data folder directly via Windows Explorer, by default this location is %AppData%/osu!/rulesets. On MacOS default this location is in application itself.
Copy the ruleset file (.dll file that you just downloaded) into the rulesets directory, do make sure that duplicate copies of the ruleset are overwritten.
Other rulesets also could share the same folder.
After completing the above steps, you may need to restart osu!lazer if it is already open. Once restarted, you should see the ruleset alongside the standard rulesets.
To update rulesets, just do the same step and overwrite the old rulesets file.