From the user detail page we can assign permission set or remove a permission set assignment

 

Go to the following path for assigning permission set to user

 

Click your name -à setup -à Manage Users -à Users à

 

1. Select the user which we want to assign permission set

2. In the permission set assignments related list, Click “Edit Assignments”

3. To Assign a permission set, select it from the available permission set box and click “add”

 

To remove a permission set assignment, select it from the Enables permission set box and click “remove” button