You might want to move items between styles/sizes in bulk. You can use the Style/Size Manager for that.

First, your items will need to be unlisted and on your Inventory page to be edited. Once there, find the Style/Size Manager. 

Go to the Sell tab at the top of the screen, then click Home. 

You'll find a new button on your Home page: 

Just click here, and find the style you would like to edit.  

Enter the new style name where you would like to move the items.  

Click Move to complete the action. Be aware this will move all items in that folder to the new folder. 

If you have custom styles created in your account, you can delete them here if they are empty.