I heard that there will be a Release Candidate of Ubuntu 17.10 on 12th.Oct. And I can’t wait for final release since I am available these two days. So I decide to install the Ubuntu Release Candidate tomorrow.
But I worry that the release candidate will differ too much with final release. And I wonder that if I install the Release Candidate one, will it update as the same with the final release?
Regards,
somebody
If you install an early build of Ubuntu 17.10:
then yes it will auto-update to become the final release.
There should not be many changes remaining at all, in theory 
Many of us have been running 17.10 for months without issue. However what works for one person may not work for another. It’s possible even the final 17.10 release may introduce some problem that didn’t exist in 17.04. So always use caution when upgrading at any time. In the least you should try out the live image on your hardware before committing to installing it.
In addition to @vanvugt’s comment you can also read the Release Notes of the final beta release. There is a section “Known issues” which lists the major issues identified.