Hello nancyjean and welcome to the HP forums!!
You have a Photosmart C410a and would like to know if you can darken the print? I will absolutely do my best to help you out with this :)
Are you wanting to darken it because things are coming out faint, or the quality is poor?
Unless you are performing a copy on the printer, there isn't really a function that tells it to print darker, so I suspect you may be having an issue with the quality the printer is producing. If I'm correct, the document that should be able to assist you is this Troubleshooting Print Quality Issues document. This will show you how to align, clean and a few other things!
Let me know how this goes for you! If I am off base as to what your actual issue is, please just provide as much detail as you can to help me understand :)