I would always set my ground floor (storey 0) to zero height (Project Zero).
Then as Ling mentioned set the altitude (sea level height) as a negative value (-254600 in your case).
If you adjust this now your model should adjust too.
But you will also have to adjust the 'height to next' of the ground floor back to 230 as show in your image.
Also if you have any 2D annotation in elevations and sections, you will have to manually move that down to match the new model position.
This way, all levels can be based from project zero (your ground floor which is at zero height) and if you need to, you can reference to sea level or the other 2 reference levels that you can set (in Project Preferences).
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We also have project zero at zero always. It is much easier to adjust the sea level (or in our case custom level since we use 'NAP' (Amsterdam Ordnance Datum)) when you inevitably decide to change your level slightly over the course of a project.