How can I dispute a parenting plan that was put into place 2 years ago?

If something has changed which has made the current parenting plan unworkable or no longer in the interest of the child, then you can file a motion with the original court to modify the parenting plan.  Before you do so, make sure that you have an argument ready to justify the change.  The courts don't like multiple changes to a plan "just because."  If the children have changed, or if the needs of the children have changed, then your argument needs to reflect how a modication will address the changes in the needs or welfare of the child(ren).