OPatch Windows
Assuming that you have downloaded the latest OPatch from Oracle. Let's see current version of OPatch utility.
C:\Users\Administrator>opatch version
OPatch Version: 12.2.0.1.15
OPatch succeeded.
Here are steps to replace OPatch.
1. Rename Old Opatch
Here we backup the original OPatch folder by renaming it.

Renaming OPatch folder - Windows
2. Unzip New Opatch
In this step, we're going to extract the new OPatch to ORACLE_HOME directory.
Right click on file, then click "Extract All"

Extracting New OPatch - 01
Enter the patch of ORACLE_HOME, then start to extract

Extracting New OPatch to ORACLE_HOME
3. Check Result and Version
We should check the newest OPatch in file manager.

New OPatch Unzipped
C:\Users\Administrator>opatch version
OPatch Version: 12.2.0.1.29
OPatch succeeded.
For Linux platform, you should go for: How to Replace OPatch.