I've experienced this twice. The first time we did this, it was done quickly. We focused on updating the collateral and training the field, but we needed to do more with current contracts, SKUs and customers. The second time around, we timed the update around a major release that introduced big improvements/enhancements as well as a UI update. This second round also involved collateral update, sales training, and customer marketing/promotion. Timing the update with a release and new look-and-feel improved the knowledge transfer and retention/recognition of the re-branding. It probably also goes without saying, but videos are very helpful and highly consumed. If there is the ability to create a promotional video and a guided "how-to" video that shows a before/after scenario it is very helpful in making a smooth switch.