If you have changed some information in your listing profile/ template and now want to reflect that change in your active listings please follow the steps outlined below.
For eBay listings:
Please select settings-> Channel integration-> edit eBay-> listing profiles-> other actions-> 'update all changes to eBay'
For any other marketplace:
Please select Inventory-> Inventory & Listings-> Manage listings-> Use the filter tools to search for the marketplace you wish to update-> bulk select your products-> select update to channel