Typically, processes and objects aren't deleted. They're retired from the System tab. However, if you need to delete an object/process and you're allowed to do so according to your organization's auditing policies, then you basically just need to archive the logs associated with that object, and then you should be able to delete the object.
Looks like this Support article explains it well so I'll it explain:
http://portal.blueprism.com/customer-support/support-center#/path/1438699282------------------------------
Dave Morris
3Ci @ Southern Company
Atlanta, GA
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Dave Morris, 3Ci at Southern Company