Hi Falcon500
You do NOT need to delete your baseboard.
Converting to 5m grid is done as follows (for 09 anyway):
Load the map into Surveyor.
Use the Save As tool to save a new version (this allows you to go back if you need to).
Go to the board you wish to convert.
Open the Topology Tab (F1).
Click RMB on the Extend Baseboard tool.
A new window will appear with a single setting to change the grid size. Change it to 5m and then click on the checkmark.
Now Click LMB on the baseboard that you wish to change. A message will come up if you wish to proceed, explaining that you cannot use the undo tool to go back to the 10m grid. Click on the checkmark to proceed.
You will now have a baseboard with 5m grid. You will, however, need to go in and retexture it. The textures will still be placed, however they will have lost their blending and rotation. You should still be able to use the get texture tool to obtain each texture as needed. It's best to do the process one board at a time, so as to keep your sanity.
Changing to 5m grid will only change the ground textures, as well as possibly require some extra smoothing on hills. Beyond this, you should not need to change anything.