Can we remove namespace prefix in salesforce? Because I have not seen any option available there in salesforce
Once a namespace prefix is created, it cannot be changed or deleted. The workaround is to move all your code to a new Developer Organization, where you can setup the desired Namespace Prefix.
Please refer to the Product Manager's post on the Community Board: How to change the namespace after package creation?
Please refer to the IdeaExchange post for a suggested change to the behavior of this feature: Cannot remove/edit Namespace prefix, once defined for Managed Apps