Since the August 31, 2011 Cumulative Update, it is no longer required to install the SharePoint Foundation Cumulative Update before proceeding with SharePoint Server Cumulative Updates. This greatly eases the burden of applying Cumulative Updates and Service Packs.

The high level process for updating your SharePoint Farm is as follows:

1) Verify your current patch level by matching the Build Number using these instructions:

SharePoint 2010: http://www.toddklindt.com/blog/Lists/Posts/Post.aspx?ID=224

SharePoint 2013: http://www.toddklindt.com/blog/Lists/Posts/Post.aspx?ID=346

2) Download the applicable Cumulative Update (CU) or Service Pack. A good recommendation is to always be one CU behind the current release for production environments to avoid issues that may be introduced by a new CU. I would treat a Service Pack the same way in that you would wait until a CU is released after the Service Pack before proceeding. Please note that updates tend to be cumulative from a certain level of Service Pack. You can find the prerequisites listed in each KB article supporting a CU or Service Pack.

SharePoint 2010 Cumulative Updates are located here: http://technet.microsoft.com/en-us/sharepoint/ff800847.aspx

SharePoint 2013 Cumulative Updates are located here: http://technet.microsoft.com/en-us/sharepoint/jj891062.aspx

3) Copy the CU or Service Pack to each of the servers that have SharePoint installed. If you are following a best practices three-tier architecture, your SQL server does not require a CU or Service Pack since it does not have SharePoint installed on it.

IMPORTANT: It is highly recommended to test your update on your development/test farm before proceeding with updates to the production environment as you will want to ensure that the update proceeded as planned and that any custom development components or third-party solutions are fully operational.

4) Run the CU or Service Pack on each SharePoint server. I generally start with the Application Server that hosts Central Administration and run the CU on all Application Servers first before proceeding to the Web Front End Servers (WFE).

IMPORTANT: Do not run the SharePoint Products Configuration Wizard until all servers have had the CU or Service Pack installed and have been reset.

5) Reset each server

6) After the servers restart, run the SharePoint Products Configuration Wizard starting with the first Application server you installed in your SharePoint Farm (generally hosting Central Administration), all other Application Servers, and finally all Web Front End (WFE) Servers. In case of failure, please review the error log presented to determine the source and note that you may need to execute the psconfig command instead of wizard. There are times when simply re-running the wizard or psconfig will configure the server properly. Use the following instructions to run your Psconfig commands: http://technet.microsoft.com/en-us/library/cc263093(v=office.14).aspx

7) Reset each server

8) Verify the build number by using the following instructions:

SharePoint 2010: http://www.toddklindt.com/blog/Lists/Posts/Post.aspx?ID=224

SharePoint 2013: http://www.toddklindt.com/blog/Lists/Posts/Post.aspx?ID=346