You need to write a server side script to go through all the users and update their urls.
Something like the following should work.
var db = require('./database'), user = require('./user'), async = require('async'); db.getSortedSetRange('users:joindate', 0, -1, function(err, uids) { async.eachLimit(uids, 50, updateUserImage, function(err) { console.log('done'); }); }); function updateUserImage(uid, next) { user.getUserFields(uid, ['image', 'gravatarpicture', 'uploadedpicture'], function(err, userData) { // do your update here, can check current data from userData user.setUserField(uid, 'gravatarpicture', 'some_new_url', next); }); }