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);
});
}
