The current Heaven is in the angelic realm, distinctly separate from earth (though likely having more earthly qualities than we often assume).
But the future Heaven will be in the human realm, on earth. The dwelling place of God will be the dwelling place of man. That dwelling place will not be where believers go now when we die. It will be in a resurrected universe. Heaven, God’s dwelling place, will be relocated to the new earth (Rev. 21:1-3).
The New Jerusalem which was in Heaven then comes down out of Heaven from God. Where does it go to? The New Earth. Then “the dwelling of God”—which means Heaven—will be with men in their realm: earth.
“Heaven” can refer to the place we go at death, the intermediate state where we live until the resurrection. But the ultimate “Heaven” is the one spoken of in Revelation 21-22. It’s the new cosmos where we’ll live forever, after our resurrections. Since Heaven is God’s dwelling place, when God chooses to relocate on the New Earth, he will bring Heaven with him, expanding it to include the new universe.
Several books on heaven state that the New Jerusalem remains “suspended over the earth.” But the text doesn’t say this. John watches it “coming down” from Heaven. There’s no reason to believe it stops before reaching the New Earth. The assumption that it remains suspended over the earth arises from a misguided instinct that Heaven and earth must be kept separate. But Scripture demonstrates that in fact they will be joined. God’s eternal purpose is “to bring all things in heaven and on earth together under one head, even Christ” (Ephesians 1:10).
Wayne Grudem, in his Systematic Theology says, “Heaven is the place where God most fully makes known his presence to bless.” He then asks an important question: “Can that place change? Yes. It has to a certain extent and it will dramatically. Because heaven’s location will be shifted to the new universe, centered in the new Jerusalem, located on the new earth.”
For more information on the subject of Heaven, see Randy Alcorn’s book Heaven.