Acrylic paintings can be altered so easily by using a glaze.
What is a glaze? It can be used over an underpainted surface to either soften an area by using a more opaque paint or a transparent paint to enhance or change the temperature.
Using transparent acrylic glazes can transform a work from ho hum to wow. the trick is to know your transparent colours. Here I am using Nickel Azo Yellow from fluid paint from golden.
Make sure surface is try before glazing and use a soft brush such as Silverwhite