I am getting the following error while trying to unistall ublogsy from umbraco installation 4.7.1.

Error details:

Server Error in '/' Application.
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Can't delete a Document Type used as a Master Content Type. Please remove all references first!
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentException: Can't delete a Document Type used as a Master Content Type. Please remove all references first!

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[ArgumentException: Can't delete a Document Type used as a Master Content Type. Please remove all references first!]
umbraco.cms.businesslogic.web.DocumentType.delete() +252
umbraco.presentation.developer.packages.installedPackage.confirmUnInstall(Object sender, EventArgs e) +1350
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +118
System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +112
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5563

Is there anything I have to do manually before removing this. I have few users created with permissions set on these nodes.

Do I need to disable them before uninstall this package.

Thanks,

Rajeev