If gravity is opposite to matter, how do you eliminate matter to gravity?

I'm not sure that your question makes sense. Gravity is not opposite to matter, gravity has an affect on matter in ways such as it has more influence over an object (a collection of matter) depending on its size, the bigger the object the stronger the gravitational influence.

The only thing opposite to matter is anti-matter, and fortunately there is not much left of it in the Universe as it has all but been eliminated in the early years of the Universe when it was in its youth. I say 'fortunately' because if it was in abundance today, it would almost certainly be catastrophic!

I hope this answers your question, if not please rephrase it and re-post it.