Hi ,
you can refer release notes[ flowchart on page 8 and page 13] which will clear the doubts
http://www.cisco.com/c/dam/en/us/td/docs/telepresence/endpoint/software/ce8/release-notes/ce-software-release-notes-ce8.pdf
you can download CE8.3.0 from below link of size 956.79MB
https://software.cisco.com/download/release.html?mdfid=284091229&softwareid=280886992&os=&release=CE8.3.0&relind=AVAILABLE&rellifecycle=&reltype=latest&i=!pp
regds,
aman