Befor doing these steps you should exit XDM if its already running. To exit XDM goto File->Exit from XDM window.
If you are on Windows:
1. Open command prompt from the start menu (type cmd to search in start menu)
2. Type C: and press Enter
3. Then type cd "C:\Program Files (x86)\XDM" and press Enter.
4. If it shows error like folder does not exists then type cd "C:\Programs Files\XDM"
5. Now type "jre\bin\java" -jar xdman.jar
On Linux:
1. Open terminal
2. type cd /opt/xdman
3. jre/bin/java -jar xdman.jar
On Mac OS X:
1. Open terminal from Applications->Utilities
2. Type cd /Applications/xdm.app/Contents/MacOS/
3. jre/bin/java -jar xdman.jar