Draining a Megaflo system

Hi

I want to change a radiator to a towel rail in my bathroom and want to know how to drain the heating system.

I have an unvented Megaflo cyclinder (upstairs) Ideal Logic 15 boiler (downstairs)

I have instructions on how to drain down the Megaflo but after that what is the process to drain down the radiators ? Is it just to find a drain point downstairs and drain the system down via that ?

Also - I have small (maybe 15mm) pipes to all rads - do I need to drain down or can I open taps to reduce pressure and use push on caps ?

Thanks Nick