I came across to not knowing how to delete unused account on RStudio Workbench and how to make myself admin to have same permissions. If someone knows this, please help me 
It is not currently possible to delete users from Workbench, but you can lock them so that they don't use any licenses or resources. Here's how:
To make a user an admin (presuming you have command line access to the server), you can use the rstudio-server set-admin command.
https://docs.posit.co/ide/server-pro/reference/rstudio_server_cli.html#user-management
Otherwise, use the Administrative Dashboard.
https://docs.posit.co/ide/server-pro/server_management/administrative_dashboard.html
If that doesn't get you what you need, please get in touch with our support team! As a Posit Workbench customer you're entitled to professional support. support@posit.co