Up to date is an adjective meaning modern or current.
In the simplest terms, if you update something you bring it up to date.
'Update' is a verb which can mean to improve, revise, modernise, bring up to the latest specifications, equip with the latest version of software, or add the latest information.
If something is 'updated' there has always been a CHANGE of some kind to bring it up to date. However, something that is up to date has not necessarily been through a process of being updated.
So, even though the two terms are related, they are not interchangeable.