I posted this in the EMET thread, but I'll post it here too:

I've been testing 5.1 and I like it. I can enable more mitigations than in 5.0, mostly StackPivot.

Good to know:
I had lots of problems with 5.0 and I've now learned that EMET itself is not necessarily the reason for these problems(crashes). It's very likely that another security product is causing conflicts. In my case it was the HIPS functionality in my AV software. With that disabled, or at least the dll injection/monitoring part of the HIPS, I wouldn't have had to disable ANY mitigation for the "Popular Software" import XML file in EMET 5.1

Latest Patch Tuesday(Windows Updates - November) might cause incompatibility issues with EMET 5.0

If you are using Internet Explorer 11, either on Windows 7 or Windows 8.1, and have deployed EMET 5.0, it is particularly important to install EMET 5.1 as compatibility issues were discovered with the November Internet Explorer security update and the EAF+ mitigation. Alternatively, you can temporarily disable EAF+ on EMET 5.0. Details on how to disable the EAF+ mitigation are available in the User Guide. In general we recommend upgrading to the latest version of EMET to benefit from all the enhancements.

Does EMET 5.1 install over the old version or is removal of the old version required before installing the new version?

Thanks.

Hey Chris,

EMET 5.1 installed over and replaced EMET 5.0 for me. :)

As brink stated, you should have no problems doing a inplace upgrade.

EMET 5.1 installed fine over the old version. Thanks for letting me know.

Usually all minor upgrades will work, but also some major upgrades. For future reference, check the User Guide - section FAQ at the end:

Is my configuration from EMET 4 compatible with EMET 5?
Yes, EMET 4 configuration is compatible with EMET 5.

I have EMET 4 installed. Should I uninstall it before installing the new version?
You don’t need to uninstall EMET 4 before installing EMET 5. EMET 5 installer will automatically uninstall EMET 4 and install EMET 5. The Configuration Wizard provides an upgrade experience to safely migrate current settings from EMET 4.

I have an old version of EMET installed. How do I upgrade to EMET 5?
If you have a version of EMET older than 3, it is recommended that you first uninstall the old version via the Windows Control Panel, and then manually delete the HKLM\Software\Microsoft\EMET and HKLM\Software\Policies\Microsoft\EMET keys.
If you have EMET 3 or EMET 4 and want to upgrade to EMET 5, you can run the installation package and follow the instructions to either maintain your old configuration or apply the recommended one.

So it can upgrade even an EMET 3 version.
In my case I'd created a batch file in the EMET 5.0 folder. After upgrade to EMET 5.1 I noticed I still had a 5.0 folder and thought something went wrong. But when I looked inside it all that was there was my batch file. Nice to see it removed everything but my own file

Tried to update again from 4.1. Launching any application covered by EMET results in a popup that so and so exploit is detected, and closing that application. Went back to my newly created system image and back on 4.1, working fine. Can't be bothered to troubleshoot when the same settings on 4.1 work fine. A Guy