Upgrading from 8 -> 10; wrong architecture...
 

I clicked on i386 instead of x86 64. The box is laptop AMD64, and I stopped the upgrade at this point:

Should I continue it and change later? Or delete files and start again?

I have no idea how fedora handles this kind of updates. But I'd stop right now, and choose the correct architecture.

Note that all the package will need to be downloaded again anyway, since all the binaries that you have downloaded till now are for i686 (32 bits) and not for x86_64. So, there's no gain in letting it end.

I would not even try to upgrade 8 to 10 ( skipping 9) there are WAY too many changes in 10
see the fedora 10 release notes .
http://docs.fedoraproject.org/release-notes/f10/
http://docs.fedoraproject.org/release-notes/f10/en_US/

rhgb is no more "Plymouth" replaces it ( unless dual booting )
NO xorg.conf in 10
ipv4,ipv6 are different in 10

Do a fresh install

What's up i92...

Does it matter what architecture I have already? FC8 install from factory disk/FC8/RHEL Bible?
Do I need to delete the files that have downloaded so far?
Where are they?

those packages are only in /tmp

Upgrading directly to FC10 should work. You need the interim FC9 upgrade only if you want to upgrade on a production server with minimal downtime.
Your new attempt should replace both the old FC8 files, as well as the bogus FC10 file for the other architecture. If you do not want to take risks, then run a clean install - if your /home directory is on it's own partition, then exclude that one from reformatting.

Debian

its possible
try yum clean all
download and install (yum -Uvh)
fedora-release-10-1.noarch.rpm
fedora-release-notes-10.0.0-1.noarch.rpm
yum clean all again
then yum -y update should take care of it