Sagemath upgrade not recognised as option in Sagemath v.9.5.rc4

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Hello there, I have been trying to upgrade my Savemath dev version from 9.5.rc4 to 9.6.rc4 with the upgrade option. it seems like the option isn't available.. when I run ./sage --help it says use the --upgrade version but it doesn't work. Is there another way to get from 9.5.rc4 to 9.6.rc4? Below is a short transcript of what I did:

    user@debian-s01a:~/sage-9.5.rc4$ ./sage --upgrade 9.6.rc4
    response: Error: unknown option: --upgrade.

    user@debian-s01a:~/sage-9.5.rc4$ ./sage --help
    shortened response:--upgrade [version] -- download, build and install the given version. Here,
                             'version' is a git branch or tag name. Useful values
                             are 'master' (the current development version, this
                             is the default) or a version number like '5.13'.
    user@debian-s01a:~/sage-9.5.rc4$ ./sage --upgrade '9.6.rc4'
    response: Error: unknown option: --upgrade.