Usage: Extract to (create the folder) C:\LM3D.CD\. If you're using DOSBox, you'd instead extract it to a folder called "LM3D.CD" inside whatever folder you're mounting as C:. If you have an existing save, only overwrite the LM3D.SAV file (not the LM3D.CFG file).
This should have all levels unlocked, with no completion / kill / etc stats.
EDIT: Mostly redundant now, as L3DUtils can modify an existing save to unlock all levels, without overwriting completion / records in the process.