do I have to drain radiator to replace hose

 

When I replaced my top hose about a year ago I simply placed a pan under the radiator drain tap located underneath and drained off sufficient coolant to lower the level below the top outlet level on the radiator.
Replacing the hose itself is straightforward.
After fitting the new hose and tightening the clamps I refilled the coolant expansion tank to the full level.
If the drained off coolant is in good condition you can reuse it but if the coolant is old looking then a complete system renewal is far wiser.
Ensure all hose clamps and the drain outlet under the radiator are correctly tightened before refilling and of course test for any leaks afterwards with the engine at hot running temperature.
Any airlocks will require the coolant system to be burped a couple of times.