Open the asset detail view of an asset in asset explorer or in task details.
Above the preview area, open the version history for the asset.
A drop-down menu with all uploaded versions will be displayed:
Open the context menu 
on
a version which you want to turn into the current version.
Click make "
Make current" in the context menu.
The preview area reloads automatically and how shows the chosen
version's preview. Additionally, the new current version is marked
with the 
icon as the current
version.