MAke sure they can handle a sippy cup. Introduce that and let them explore it until they have success using it. It can take a few days. Have it readily available to them. Then drop one bottle feeding a week and give the cup. It takes time. You may want to let them have the last bottle for a long time. The little one I care for still has her afternoon bottle. All others have been dropped. Google weaning too.
I found these amazing sippy cups by Aveeno that have a soft spout but look like a traditional sippy. That was the only thing that has helped me get all my kids from bottle to cup. After they started using those cups, we just gradually changed to a sturdier, "regular" cup.