You can install an AdminUI 12.52PS1 only at the last step during an upgrade.
Following the upgrade guide
To migrate a CA Single Sign-On deployment with multiple Policy Servers and Web Agents,
remove one of the Policy Servers and Web Agents from the environment.
While these components are being upgraded, the remaining Policy Servers and Web Agents
continue to protect your resources. Continue removing and upgrading components until all
components are upgraded or operating in mixed-mode compatibility.
Complete the following procedures to migrate from r12.x to 12.52 SP1:
1. If your environment includes multiple instances of smkeydatabase, synchronize all instances. Part of the Policy Server upgrade includes migrating all content in the smkeydatabase to the certificate data store.
2. Upgrade an r12.x Policy Server to 12.52 SP1.
3. Upgrade an r12.x Web Agent to 12.52 SP1.
4. Upgrade the remaining r12.x Policy Servers and Web Agents to 12.52 SP1, respectively.
5. Upgrade the r12.x policy and key stores to 12.52 SP1.
If you are using FSS Administrative UI, ensure that you upgrade Policy Store to 12.52 SP1 as Policy Server and Policy Store must be of the same version.
6. Upgrade the r12.x Administrative UI.
7. If required, use the Administrative UI to save existing reports locally and remove the r12.x Report Server and report database from the environment. The simplest path to an 12.52 SP1 reporting environment is to install and configure a new Report Server and report database.
>> We can see the Upgrade the r12.x Administrative UI is at the last stage !