If you want to upgrade external libraries you need to go to platform's
server-lib/external directory. Different library providers has different directory for libraries. They are created just for better readability. You can create your own directory here if you want.
To upgrade library just find jar files you want to change. Then remove it and put new jar you want to be. Remember that these libraries are used for server and for all microservices.
Remember also to change your pom files to use same libraries' versions as the one located on server (it is very important for libraries with scope