Installing SQL Server 2008 R2 Service Pack 1 I have SQL Server 2008 R2 installed on my computer. I want to install Service Pack 1 for SQL Server 2008 R2. Do I need to select upgrade option or new installation during installation of service pack or remove current installation and install SQL Server again. 

I am trying to select "new installation or add new features" on first page of installation and then  selecting current instance on next page but It is giving some error like registry value invalid.
It sounds like you're running the wrong file.

Download one of the files from http://www.microsoft.com/download/en/details.aspx?id=26727 and then run that. It shouldn't prompt you for "new installation or add new features", it should prompt you for which instance you want to apply the service pack to.