How can I represent the following situation in Use Case diagram:
User can manage account settings: change password, change language, date of birth, etc.
I want to group "change password, change language, date of birth, etc." use cases in the "manage account settings" use case. What relation should be used here?
This sounds a lot like a homework question. Wikipedia has a nice description of how to use these. Note how each of the bubbles in the example refer to actions that actors take and their interactions. Use cases are almost entirely about user-facing information.
In reality, Manage Account isn't a legit use case at all.
Use cases should stand alone. In other words, the system should yield something of value to the actor if the use case in question was the only use case that the system provided.
"Manage Account" wouldn't stand alone. That is, no one would create a system that only allowed a user to manage their account.
But if you had to model the situation you described for homework purposes, it would probably look like this:
Use Case Relations semantics can be sometimes fuzzy, it's up to you to be consistent. For example your case could be similar to this case:
