With release 1.17.10, your Realms or Realms Plus subscription now lets you have 3 worlds loaded into your Realm server at the same time (of which only 1 is active at any given time). Previously, your Realm settings included settings for the Realm/subscription and for the (single) world loaded into it on the same screen, available by clicking the pencil icon next to your subscription. Now that there are 3 separate worlds, each with its own settings, the settings screen is broken into Realm settings and 3 World settings screens.

The Realm settings include the Realm name and description. From here you can also change your invite code, send invites, manage your member list and permissions, manage your subscriptions, manage your Xbox Live club feed, and open/close your Realm. The Realms settings are accessed by clicking the pencil icon, then choosing the Manage Realm button at the top.

The World settings include the world name, difficulty level, game mode, and backups. From here you can also activate cheats, download or upload (replace) the world, reset the world, restore a backup world, and manage the world's add-ons. The World settings are accessed by clicking the pencil icon, choosing the picture button for the world you want to edit, and clicking the Edit World button that appears.

Note: Currently, if you click the Edit World button for an inactive world, it activates the world instead of opening the world settings. That is, it functions exactly the same as the Active World button that also appears. This is probably a bug, but it's not the bug described in this ticket.