It is safe if done properly.
The overall procedure is:
-Download the correct patch package.
-Make a copy of your live site.
-Install the patch package on the copy site.
-Make any database changes required on your copy site.
-Test it thoroughly.
-Backup your live site.
-Install the patch package on your live site.
-Make any database changes required on your live site.
-Make any other changes required
-Check your live site to make sure it is working correctly.
This link has detailed instructions including how to unpack/upload the upgrade.
http://docs.joomla.org/Upgrade_Instructions