To update SharePoint to Service Pack 2:
1. Install SharePoint Server 2010 Service Pack 2 on all of the SharePoint servers in the farm. The installation of the binaries can be done in parallel, or sequentially.
2. If necessary, install the Office Web Apps 2010 Service Pack 2 on all of the SharePoint servers in the farm.
3. Install any necessary Language Packs on all of the SharePoint servers in the farm. When downloading Language Packs, make sure to select the appropriate language from the drop down and wait until the page appears in the desired language before clicking the Download button
PS: If you have Project Server 2010, make sure you read this post from the Microsoft Project Support Blog:http://blogs.technet.com/b/projectsupport/archive/2013/07/23/project-2010-and-project-server-2010-service-pack-2-sp2-released.aspx
4. Now that the binaries are installed on all the servers, it’s time to go to the more stressful part which is running the SharePoint 2010 Configuration Wizard. On any one of the SharePoint servers, start and run the “SharePoint 2010 Configuration Wizard” as an administrator. In the Configuration Wizard, it may ask you if you want to change anything. At this time, do not change anything, simply click next, next, and next. If you cheated in any of the previous steps, you will have an error in this step!.
5. After the Configuration Wizard is done running on the first server, run it on the next SharePoint server in the farm! Repeat Step #5 until all SharePoint servers are upgraded.
6. Time to test everything!
You are done and successfully installed SharePoint Server 2010 Service Pack 2 using the best practices from Microsoft!