My under grad was in AI and my PHD was in robotics. Good start would be to look at appropriate masters courses combined with as much math and statistics as you can stomach.
AI is a huge field, as is robotics. So you probably want to specialize. Are you interested in topics such as automated reasoning and theorem proving, control of dynamic system, statistics and machine learning, computer vision, signal processing, optimization, metaheauristic search, probabilistic inference, multi agent systems, swarm intelligence, natural language processing, symbolic systems, operations research, mechanics, localization and mapping, cognitive systems? They are all fairly different although with some overlapping concepts (math and statistics tend to crop up everywhere) and if you are limited in time then I would concentrate on a small subset.
There are some good online resources and books for some subsets. Artificial Intelligence a Modern Approach is an excellent book that covers many concepts.