Hi @Hareesh_Katta and welcome to the community.
Can you please clarify a bit your question?
If it is related to name listed, the users have to go through their profile to change it (refer to How to Control Your Profile Settings in Asana | Product guide • Asana Product Guide). If else, please let’s discuss when you’ll have ad a few more details 
@Sebastien_Levesque
Thanks for your response @Sebastien_Levesque
My issue while is when I am assign the task. Not related user of the project also displaying .
Note : I removed the added user in the group. But still while I am assign the task to the user. Unrelated project users are coming.
Hi @Hareesh_Katta and welcome to the Forum! 
When you assign a Task, the suggested assignee list in the drop-down menu will show you everyone who’s a Member or a Guest of your Organization, whether or not they’re actually a member of the project this task is nested.
With that said, if you want to remove a Member or a Guest from your Organization you can follow the steps on this article: Setting up an organization in Asana | Product guide • Asana Product Guide
I hope that helps! Let me know if you have any follow-up questions!
Hi Natalia.
I don’t get it, I followed the steps in the guide you linked, and I can still attribute tasks to people that shouldn’t be there anymore. I even deleted the whole team and created a new one with me being the only member on it, still no luck. I am missing something ? Thanks in advance.
Hi, this solution is for inviting to the team. I need help removing them from my dropdown completely.