Paint has its place, but not on your aluminium windows. Paint accidents happen, and sometimes a paint project will seem OK, but once it is complete, you see that is not what you wanted. Removing paint from your aluminium windows is a task that must be completed slowly. For accidents that just happened, the paint is easily removed. For other situations, the right tool and patience are needed.
Wipe away any dust or dirt from the aluminium window containing the paint with a soft rag or towel. Wear goggles and rubber gloves.
Tilt your dull putty knife so that it is at an angle, and slowly scrape paint from the aluminium window. If you don't have a dull putty knife, wrap a rag around the blade of the putty knife and then scrape the paint from the window. Using a rag on the putty knife will require extra pressure to remove the paint. Don't use too much pressure--you don't want to scratch the aluminium.
Continue scraping until the paint is removed from the window. Next, spray some WD-40 on a rag and polish the aluminium on the window. Wipe the window thoroughly. Then apply another spray of WD-40 to a rag and wipe the window again to finish the polishing process.
If you are painting around an aluminium window and accidentally get some paint on the frame, just wipe the paint off with a soft rag and then polish with some WD-40.
Always wear eye protection and gloves when removing paint from a window or other surface.