After the download is complete, drag the downloaded .jar file to an open instance of Astah. A pop-up will appear asking you to confirm installation, choose [Yes]. If the pop-up below opens restart Astah.
If you see the [yUML] option under [Tools], the installation is complete!
How to Use
Open a project file that includes the diagrams you want to convert to yUML and then go to [Tools] – [yUML] – [Convert to yUML diagrams].
[yUML diagram viewer] appears. By clicking [Copy], you can copy the text that represents the diagram for yUML.