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1. Choose the "Archive Version" option on the Actions menu next to the version number in the top right corner of the Test Details web panel on a Test issue.
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2. Once the version is archived, a lozenge will appear next to the version name, indicating the selected version is archived.
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The unarchive version action is the opposite of archiving and can also be found on the same Actions menu next to the version number in the top right corner of the Test Details web panel on a Test issue.

You can also archive Test versions from the manage versions dialog. 

Executing a Test version

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Delete a Test Version