It maybe that the updates certificate has expired, this can be overcome.
download the update from here, Download OS X Lion Update 10.7.5 (Client Combo) once downloaded and before you try to install it open System Preferences> Date & Time uncheck Set date and time automatically, now change the date manually try something like 1st of February 2013. Once you have changed the date try installing the update. If it installs then you might need to install this, OS X Lion 10.7.5 Supplemental Update again keep the date to the altered one. After the updates have been installed successfully then you can set the date back to today and check the Automatically update date and time.
Kappy's response is to upgrade to High Sierra, as you are on Lion (10.7.5) you can't upgrade directly to High Sierra you would need to upgrade to El Capitan first. Depending on the age of your Mac you may or may not be able to upgrade to these newer OS's check the specifications lists in the How to's.
How to download OS X El Capitan - Apple Support
If you do want to upgrade your Mac to a newer OS check that any third party software you use has updates so they will continue to work in El Capitan or High Sierra, also check that any printers/ scanners etc have newer drivers and software available so they can still be used in the newer OS's.
If you decide to upgrade make sure you have made a full back up of your MBP on an external drive.
