First Time Upgrading

[SuperStyle5]

I have a AMD64 Quad Core 64bit running FreeBSD 6.4, I set it up so it runs the mail server (and all mail backups) for my fathers small business, I run several large mysql databases via it which are key to the intranet I created for his chain of shops to communicate.

I am still new to FreeBSD/Linux/Unix etc how hard is it to remotely upgrade the server from 6.4 to the latest version (7.x) without causing any major issues?

We run: Mail w/smtp/imap/pop3, web server w/php & mysql and use it to store backups.

 

[ale]

Probably it would be easier to do a backup of your data, do a fresh minimal 7.1 install, reinstall the needed ports after updating your ports tree and restore the data.
This way you can more or less have an idea of the time needed.
Theoretically an upgrade should be feasible and with a high probability of success. And I really hope that for you.
Anyway I always think that it's better to be prepared for the worst.
If the upgrade fails for any reason, you may not know how long it will take to fix your system, expecialy if you are, as you said, still new.
Probably the easiest way, especially if you are running GENERIC, is using freebsd-update:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/updating-upgrading-freebsdupdate.html
Anyway, being a "production" system, I wouldn't work remotely, but this depends on many factors e.g. how long can be the downtime, how long it will take physically reaching the site in case of disaster, etc.

P.S.
Doing a rapid search I've found this one:
http://www.daemonology.net/blog/2007-11-11-freebsd-major-version-upgrade.html

P.S.S.
Attempting a remote upgrade shouldn't suggest you to skip backing-up your data.

P.S.S.S.
I hope the link on P.S. is not too outdated.
I have no experience using freebsd-update as I've always upgraded from sources.
You may want to hear other bells here before proceeding.