In case you mean the labels under: Administration > Label & Messages
you need to restart your application for the changes to take effect.
If not the case, would you please provide more information about the labels you are trying to amend?
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items