How do I repaint a steel door previously paintedwith glossy oil paint

i would Sand down the door to remove all the oil paint, wasn't clean and once dry apply a primer. then you can paint your desired shade.

correctipn: should say, wash clean, not wasn't clean.

You need to do some prep work but you have help in this site: http://homeguides.sfgate.com/paint-over-oil-paint-metal-front-door-28493.html  ; Good luck!

Do you want to use the oil based paint with the repaint? If so it will require different preparation.

i think you should start with a primer like Kilz, it adds a bit of texture for your new paint and makes a nice base for a lighter color if that's what you choose.

Go over surface with 120 grit or higher sand paper, maybe even sand paper to be used with water. Use a primer paint for metal surfaces before using last coat of Rust-Oleum spray paint.