Hi,
This will only affect new players you create, the current ones can be upgraded via Studio one by one or by running this query directly:
mysql> update ui_conf set html5_url = "/html5/html5lib/v2.50/mwEmbedLoader.php" where html5_url like "%html5lib/v2.%/mwEmbedLoader.php"In newer versions, this happens at each upgrade but the version you're running does not have that.