Generally Ubuntu will detect hardware at boot time. This means that any hardware changes we had made between boots will be taken care of from the next boot.
From my own experience this will work fine even when we changed a sensible piece of hardware like a graphic card. In the usual case we just plug in the new hardware, boot and may have to install proprietary drivers only in case we feel we need them for better performance.
However in some cases there may be issues from a propretiary driver we may had installed for the previous card. Also we may need to purge an altered X.org configuration if this was done from the previous graphic card's settings. This can all be done from booting a root shell in case the graphic system was badly tampered.
There is no need to reinstall Ubuntu.
To avoid sitting on a Ubuntu booting to command line only we may want to consider removing all proprietary drivers before we change our graphic card.