1. Run Cinema 4D R21 and choose "Extensions->Tools->Export License Overview...". A text file will be opened showing some license information. Copy the value displayed as systemid (omit the quotes!).
2. Go to the customer area on c4dplugin.com: https://c4dplugin.com/customer
3. On the LICENSES tab select the checkboxes of the plugins you want to update and enter the systemid into the text field at the bottom and click on "Request Licenses"
4. The updated licenses are displayed in green. Download the license files using the appropriate buttons on the right and save it to the preferences folder of C4D. You can locate this folder easily by openening the preferences in the C4D app and clicking on the button at the bottom. The file must be stored in the top level of the folder "Maxon Cinema 4D R21_XXXXXXXX"
5. Close Cinema 4D and return to the cutomer area. On the DOWNLOADS tab download the latest package of your plugin software. The installation is described in the pdf doc included.
6. Run Cinema 4D R21. The plugin should appear in the Extensions menu (there is no Plugins menu anymore).