After coffee has been roasted and ground, there is no way to remove the caffeine, at least in a way that could be done at home and leave you with grounds that would make good tasting coffee.
You may have heard of the Water Method of caffeine extraction. This is the first way people learned to make decaffeinated coffee. It happened as an accident at first, coffee beans that were being transported by old sailing ship became fouled with salt water. Not wanting to lose the cost of the beans being shipped such a far distance, the ship's crew just dried out the beans and used them as normal. Those coffee made from those beans turned out not to have the 'kick' that it normally would.
The caffeine in coffee beans is soluble in water when heated to above 175 degrees before roasting. They often use other chemicals to complete the process as using only the Water Method might lessen the quality of the resulting coffee. The beans are dried and then roasted - and in most cases, ground up before they even get to you.
So no, I'm sorry - no way to remove the caffeine from that can or bag of already roasted and ground coffee now. For complete details, I put a link below that explains the entire process and what chemicals are often used in the process.
I hope that helps.
