Delete all previous versions of all Artifacts in environment in one execution

You can delete the objects at the folder level. From design, go to the folder which contains your objects. Select all objects at one go and click on delete.

Hi Aditya, i want only previous versions of the objects to be deleted not the objects.

Sorry, I thought the objects.. 
You can do bulk deletion of versions by providing filter criteria in your version dialouge box.
When you select a filter criteria, it returns multiple versions and a message appears that asks you if you want to delete the filtered versions (i.e. all the rows returned after applying the filter). If the latest version is included in the filtered results, it will not be affected by the bulk deletion.
So this way you also keep the original version.

That is the only way. Else you can look for some plugins.

Sorry, I thought the objects.. 
You can do bulk deletion of versions by providing filter criteria in your version dialouge box.
When you select a filter criteria, it returns multiple versions and a message appears that asks you if you want to delete the filtered versions (i.e. all the rows returned after applying the filter). If the latest version is included in the filtered results, it will not be affected by the bulk deletion.
So this way you also keep the original version.

That is the only way. Else you can look for some plugins.