The easiest way of upgrading Jumi module or Jumi plugin is overwriting old extension files that resides on the server with new ones from the new distribution package.
However there can be more substantial changes between Jumi version. In that case the twin "uninstall old extension" - "install new extension" applies. Bear in mind that written scipts in the jumi module and in the component will be lost in that case.
If you want to preserve Jumi component scripts then backup jumi database table before upgrade and then restore it..
Read the ChangeLog or Release Notes that can be found in the distribution packages.