Hi @Jessica Wilkinson ,
According to the error, it may be related to the account you log in to the computer, please first ensure that the account you used is an Administrator account with the following permissions:
If you still couldn't uninstall exchange by this way, we could tried to uninstall Exchange server in unattended mode like below to check if there are any errors there:
Setup.exe /IAcceptExchangeServerLicenseTerms /mode:Uninstall
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