If you do not have automatic updating turned on, or to check whether you need an update, go to Windows Update by clicking the Start button, All Programs, and then click Windows Update. In addition you can go to Microsoft Update. Microsoft Update is an online tool that will scan your computer and provide you a report about what updates your computer needs.
Read more about April’s updates here – http://www.microsoft.com/en-gb/security/pc-security/bulletins/201204.aspx