Auto increment primary key in SQL Server Management Studio 2012

Question

How can I make a SQL Server database table's primary key automatically increment? I searched the forum but couldn't find a way to accomplish this.

Despite looking through the properties, I couldn't find a choice. I read a solution that said to go to the Identity specification property, set it to yes, and set the Identity increment to 1. However, that area is greyed out, and I am unable to convert the no to yes.

I'm sure there's an easy method to do this, but I can't seem to locate it.