How do you move big boulders in Pokemon white version?

You can't move big boulders in Pokemon White version. The only way to interact with them is to use the move Rock Smash which will break them into smaller rocks.

You'll need to teach Rock Smash to one of your Pokemon. You can learn it from the Move Tutor in Castelia City or from certain Pokemon like Machop, Rhyhorn, or Graveler.