Painting aluminium window frames is a cheaper alternative to removing the entire set. The key to a successful paint job is preparation. Give the window frame a thorough clean with a brush and vacuum cleaner, making sure to remove all forms of dust and debris both inside and out. If there are weather seals attached to the window frame these must be removed as well.
Masking off the area around the window with painter's tape and a plastic drop sheet will prevent over spray from marking your wall. Putting a canvas drop sheet will protect your floor while spraying. With proper preparation, you should be able to achieve excellent results. - EricL
Bunnings has helpful D.I.Y. Advice on How to update window mullions. I would certainly encourage you to use some high quality painter's tape and take the time to cover an area as wide as possible with drop sheets so you don't have to repaint anything. - Jason
We are renovating our home and I have spray painted our aluminium windows from blue/black to white. When I sprayed my very first window I was nervous but after a while you will get the hang of it. - Sooze