Easier if you unbolt the primer pump from the engine.
Then when taken off the engine, undo the 10mm bolt on the top. Pull the unti apart.
Your new filter with come with 4/5 seals. The small circle goes on the bolt at top, the 2 big ones fit in the top and bottom of the housing and the other little one goes under the filter around the bolt hole.
Once tightened back up, re-bolt to engine. Add the pipe from tank ONLY, press the primer until it bleeds through fresh bubble free diesel. Once happen connect the top pipe and start the engine.
J P Evans, February 2006