Changing your password is almost exactly the same as setting up a new Lockr. Please refer to those instructions.
After changing your password, a sync will be initiated immediately in order to upload the changed data.
If you have other devices that sync with the same database, the data on those devices will be completely replaced at the next sync.
It is not possible to perform a full record by record sync on databases with differing passwords.
For this reason, before changing passwords, ensure that all devices have their individual changes synced before doing so. After changing the password, it is recommended you ensure that the sync has been performed and then sync your other devices to download the changes.