Where did I mention about a "completely new computer"? Did I not say "a new HDD"? HDD means hard drive. Buy a new hard drive, insert it into your old computer, make a fresh install of FreeBSD along with all the ports and packages you need, then copy your configuration and home directories.
I'm no judge about that . But following my suggestion you'll keep your old installations working and untouched and will always have the option to run it, should something not work OK with the new one.

Gentleman, here is a status update. I elected to do a step-by-step
metamorphosis of my FreeBSD 6.1 system to an 8.something system, the
first step being the upgrade from 6.1 to 7.0 that was laid out in
detail by user "vermaden". It almost worked. I got as far as the

make installworld

command, which, you will recall, is the second-to-last command. The
command that failed was the very last command:

mergemaster -FiU

which is failing with the error message:


mergemaster version 1.54.4.1
Usage: mergemaster [-scrvahipCP] [-m /path]
[-t /path] [-d] [-u N] [-w N] [-D /path]
Options:
-s Strict comparison (diff every pair of files)
-c Use context diff instead of unified diff
-r Re-run on a previously cleaned directory (skip temproot creation)
-v Be more verbose about the process, include additional checks
-a Leave all files that differ to merge by hand
-h Display more complete help
-i Automatically install files that do not exist in destination directory
-p Pre-buildworld mode, only compares crucial files
-C Compare local rc.conf variables to the defaults
-P Preserve files that are overwritten
-m /path/directory Specify location of source to do the make in
-t /path/directory Specify temp root directory
-d Add date and time to directory name (e.g., /var/tmp/temproot.0818.13.53)
-u N Specify a numeric umask
-w N Specify a screen width in columns to sdiff
-A architecture Alternative architecture name to pass to make
-D /path/directory Specify the destination directory to install files to
-U Attempt to auto upgrade files that have not been user modified.

In other words, there is no `F' option.

I recognize the validity of advising me, at this point, to read the fabulous
manual, and decide what I want "mergemaster" to do, and then select the
appropriate option. However, I do not know what I want "mergemaster" to do,
since I do not know what benefit user "vermaden" wished me to secure from
the `F' option, therefore I cannot select the option that would secure that
benefit. Also, when the stakes are this high, I hesitate to rely,
unnecessarily, on my own unguided understanding. I have a healthy respect
for my smarts, but I have no experience updating a FreeBSD system, and, as
Thomas Hobbes convincingly pointed out, experience is more useful than
intelligence. I turn to you, then, once again, and hopefully for the final
time. What is the act that remains undone, and how do I do it? The "uname -a"
command is reporting that mine is now a FreeBSD 7.0 system:

FreeBSD norman 7.0-RELEASE-p12 FreeBSD 7.0-RELEASE-p12 #2: Thu Aug 18 09:33:57 CDT 2011 root@norman:/usr/obj/usr/src/sys/GENERIC i386

but I have still not done the thing that the "mergemaster -FiU" command
was supposed to have done for me, and I do not assume that the thing can
safely remain undone.

Hopefully, once the upgrade to FreeBSD 7.0 is complete, I shall then be
able to use the "freebsd-update" command to take me the rest of the way,
and I shall have only one more post to make, the one that reports success.
In the meantime, I thank you in advance for your replies.

Run mergemaster without -F, then. You'll just (potentially) get prompted a few more times. Nothing harmful.

Back up your /etc first.

man mergemaster about "-F" option you're missing: