Hi,
1) first always make a backup
2) then here :
https://www.gavick.com/updates?task=group&id=4 - check which files has been updated
3) you can make a update even manually, just by replacing "old" files with "new" ones by FTP tool.
If you made a customizations in any of them, just do not touch them.
Whole process should take you less than 5 minutes.
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If you didn't make any changes in theme core files, yes you can also reinstall theme. But do not forget about (1)