On old pc how to replace Zorin os by Zorin lite

Hi , i have installed zorin os on a old pc and it is running very very slowlly, i would now install zorin lite on it but impossible(via new bootable usb, or deleting partition ) nothing works .
I am a new linux user perhaps my question is stu… sorry
thank for response

Welcome, herve.
Please describe your problem in more detail.
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