126.96.36.199 is the mcafee agent extension minimum requirement, you have to check that in software, extensions. 4.5 patch 3 is compatible based on that kb.
So just need to check your extension version and update if required
For upgrade process, please follow the steps as below.
1) Backup the EPO folder and EPo DB OR follow the KB66616 to backup specific folders from the backing up column.
2) Follow the KB71825 EPO checklist, this is Highly recommended.
Note: Don't ignore any step from KB71825, since it avoid failures of the upgrade.
3) Run the setup.exe file with run as admin and proceed further.
The above backup process, helps to restore, if something goes wrong.