Best way would be taking online classes through Coursera, edX or Udacity.
All 3 offer best quality material to take you to CS graduate level.
What you need to know is what the curriculum of CS degrees at good universities contain.
In terms of specific knowledge and skills, you will need to take calculus and discrete math classes. The few classes in algorithm design and analysis, data structures. You may want to take few classes in compilers, networking and operating systems in order to better understand how the whole system works. Then few classes in programming languages (not a specific language but the theory of programming language). For further advancement you may want to take some more classes in machine learning, artificial intelligence, linear algebra, human computer interaction, computer vision, database systems, cryptography etc.
It requires proper amount of time to accomplish all.
And not all CS graduates are as skilled as you think. May be you are more skilled than some of them. So before starting it would be good to understand what you are trying to accomplish by getting CS skills. May be you are good to continue with your current skills?