Download the latest version and run the installer. This will not delete any bookmarks or personal settings
Safari - Safari updates are included with Mac OS X updates. To update you Mac, go here.
Some Safe Browsing practices
Update anti-virus and anti-malware programs
Use a firewall program
Never click on pop-ups
Never respond to Spam e-mails
Never open e-mail attachments that you were not expecting. If you are ever in doubt, e-mail the sender to make sure they sent it to you or google the e-mail to see if the attachment is bad.
Never click on links in your e-mail. Instead, copy/paste the URL into your web browser to ensure that the link is not redirecting you unexpectedly. For an example of URL mis-direction, view this image.
Avoid using peer-to-peer (P2P) network programs.
Avoid using your personal e-mail address for random registrations. If you are browsing the web and come accross a form that you want to fill out, but you are not sure what it will do, you may want to use a throw away email address to fill it out with. View these Google search results for some Disposable Email services (Note: some sites disallow use of these accounts)