For Computers/Tablets/Laptops: Both Windows and the Mac OS are typically set to look for updates automatically, but it is important to regularly check the computers you use to make sure this function is running properly since viruses and other malicious programs can attempt to block updates.
For Mobile devices, phones, some tablets: Updates are usually released and/or restricted by the hardware manufacturer. Not all models may be able to run the most recent version of a mobile operating system, since the software that manages different hardware components - "drivers" - may not be compatible with a new version. To check your device look for an "About" setting or option that allows you to see what specific version it is running and whether an upgrade can be installed. Otherwise see your instruction manual, or visit the website for your specific device
For Software applications: To update a specific program, there is typically a "Check for Updates" option under its Help menu, or you can visit the company's web site for patches and new versions. You may also be prompted by the software when it opens or closes if an automatic update feature is enabled.