If you want to migrate to new hardware it is less often necessary to to reinstall your IPFire.
There are a commonly only few important things to do.
Open a CLI and start the setup-wizard.
First you have to remove the obsolete NICs before you are able to assign the new ones.
To accommodate any differences between the hardware devices, you need to remove old files for the RRD graphs and update the sensors that are installed in your system. You will know if you have an issue, as collectd will print dozens of lines to your kernel log (/var/log/messages) every 30 seconds or so, causing big log files.
Stop collectd and vnstat to get access to the real files on the hdd/flash:
/etc/init.d/collectd stop /etc/init.d/vnstat stop
Remove the "old" rrd-files within the folder "/var/log/rrd":
rm /var/log/rrd/*.rrd rm -rf /var/log/rrd/collectd/localhost/*
Rescan for the correct sensors for the new hardware:
Answer "Y" to all of the questions to generate a new configfile (/etc/sysconfig/lm_sensors).
Lastly, restart collectd and vnstat:
/etc/init.d/collectd start /etc/init.d/vnstat start
Finally a reboot is highly recommended.