Upgrade SQL server from 10.50.1600.1 to 10.50.4000.0

I've inherited a SQL server I need to upgrade to 10.50.4000.0.

I'm not a SQL guy, but from what I'm gathering it's a jump from R2 RTM to R2 SP2. Would I need to install SP1 first? Can someone point me to the appropriate upgrade exe?

Thanks,

Scott