What should I do to put new color ?I have iron old chair with 2-3 coat

Best to strip it off. You can get a wire brush attachment for your drill and get it off that way or via chemical strip.

Clean well. Use a sander or steel brush to remove any loose paint. Clean again. Let dry. Spray paint with a good quality spray paint + primer. Should work well. Keep in mind that the elements will take their toll over time anyway, so if your iron chair is outside, eventually it'll have to be repainted.

Clean and lightly sand,allow to dry,apply 2 coats of Rustoleumns2x spray paint allowing to dry in between coats.Use a Clear UV sealer

Using a steel brush remove any peeling paint. Clean well and let dry. Use a good quality spray paint + primer next. If your chair is going to be outside, keep in mind that no paint job will last forever because Mother Nature does take it's toll. You could also consider purchasing an automotive spray primer to use before using spray paint. That does have a bit more longevity.

Both are great ideas. Be sure to wear eye protection when doing either method!

Thanks

Both are great ideas. Be sure to wear eye protection when doing either method!