This method is for using an SFTP client to install a Dev build, if you would prefer to use McMyAdmin see this guide here: http://www.minecraftserverhost.net/secure/knowledgebase.php?action=displayarticle&id=142
WARNING: Only use this guide if there are no Recommended/Beta Builds available. Dev builds are unstable and can cause server lag, crashes and map corruption. If you install a Dev build you are doing so at your own risk. Please make sure to update to a Beta/Recommended build as soon as one is released.
Plugins: Some of your plugins will most likely break or not function with the new release. You can either update them or disable them until the plugin authors have updated them for the new build.
We cannot be responsible for any issues you may encounter with trying a Dev build.
Here's how you can update your server to a Craftbukkit Dev build:
You'll need the SFTP/SSH login info located in the Minecraft Server Host: Account information email you received when you purchased your server. (Note: We can't offer any help with installed dev builds.)
Once your connected go to the /minecraft folder on your server.
Next delete the craftbukkit.jar file. Now download the latest craftbukkit dev build to your computer and rename it craftbukkit.jar.
Place the craftbukkit.jar file in your /minecraft folder on your server.
Now start up your server as normal and the dev build should load.Latest Dev Build url: (Use Dev builds at your own risk!!)