If you are home-hosting the server:
1. Download the 0.3z server files
here
2. Extract the files
3. Copy and paste your server files (scriptfiles, filterscripts, includes, plugins, etc) to the new one (0.3z)
4. Don't forget to edit your server configuration files (server.cfg)
5. Run the server
If you are using a host:
There should be an upgrade option in your panel. If not, try contacting your server hosting.
If you encountered other problems, please let me know.