The first rule of troubleshooting, "isolate and identify." In other words, if you have added any hardware to your Mac over the years, remove it. I have seen RAM now recognized as "bad" by a new OS where it worked fine with the previous OS.
The comments about Safe Mode also apply as that disables third party additions to your computer. Hold down SHIFT while booting, when the Apple logo appears release shift. Booting takes longer in Safe Mode, let it do it's thing. If your Mac stops freezing then something you installed is broken under the new OS.
The 3rd thing I would try is one of the OS "cleaning" tools. I use Onyx (there are others, that's my favorite). Download it, and run the automation tool, then reboot your Mac.
Let us know the results by editing your question to indicate what you have tried.