The PA28 181 doesn't have a hinge in the middle at the top, so you have to remove the whole of the top half.
It is secured by similar catches to 161 and you have to undo them on both sides and make sure they're hanging clear, then lift up the edge close to the windscreen slightly (and note that it can be sticky on the seals ) once the back edge is free slide it forward to disengage the two locating spigots from the holes in the lower half just behind the spinner.
You can then lift it and roll it towards you and walk clear, though it's usually easier with two people.
Refit by reversing the procedure and be VERY careful to locate the front spigots properly.