Normally your Mac will be set to auto-check for software updates and these you will be notified by a dialogue box appearing from time to time, taking your through the update process.
However, if this is disabled or you want to manually check for software updates you can simply:
On the menu bar situated at the top of your screen
select the apple symbol
A drop down menu will appear
From the drop down menu simply select software update
You will then be presented with a dialogue box
Which will start seacrhing for updates for all programmes installed
When the search is completed you will be notified if any programmes or your OS needs updating
A series of dialogue boxes will appear guiding you through the process.
when updating make sure you have Administrator rights and close all other programmes that may be running
