Most of the time, in my experience, this urge is a manifestation of fear. Keep going.
If you're really, really stuck, go back to the last turning point (not the beginning) and figure out if you made a wrong turn, b/c a true writer's block (lasting several days or weeks) can be a sign of going the wrong way in a story.
If there's no serious problem with that turning point, then just keep plugging along. You might make some notes (I usually keep a file entitled "revisions" in the folder assigned to my WIP, and I put notes like "change the day when X happens," or "the hero has blue eyes, not brown," or "emphasize the theme of ___" or "change the setting for the first three chapters" or whatever), and then keep going as if those changes were already made.
Of course, some writers need to have every existing line, paragraph, scene and chapter perfect before they can write the next word, and if that's your style, then you have to go with it and forget about anyone else's style. But for most writers I've known, the urge to rewrite is a form of procrastination and fear.
JD