Hello - Just a really stupid question but if I update Joomla to the latest version will it effect any K2 files?

I ask because my K2 is heavily modified and don't want anything overwritten if I do an update.

Backup before upgrade!
Your modifications should be in overrides of K2 in order to be upgrade safe
Joomla upgrade should not touch any k2 files, although you should update all templates, extensions and plugins prior to upgrading joomla so as not to have problems.
That would include k2 if you havent hacked the core of k2

Thanks William.....

How do you mean hacked the core?

I ask because my K2 is heavily modified and don't want anything overwritten if I do an update.

Have you changed any k2 core files?

Updating only Joomla! will not affect K2's files but if you have edited core files there is a chance that your edits won't play that nice with Joomla!'s newer versions.