The principal is relatively easy depending on whether you want a Azure WebSite or Cloud Role - for Cloud...
- Ensure you have the Azure SDK installed from the WebPlatform Installer.
- Add a WCF Cloud Service Role to your project
- Expand the out the project and right click onto the 'Roles' node selecting 'Add' and then existing project from your solution.
- Publish the role using your Azure credentials.
These two articles provide an end-to-end tutorial that goes into more depth...
- http://www.claudiobernasconi.ch/2013/08/03/deploying-a-wcf-service-on-windows-azure/
- http://blogs.msdn.com/b/nishasingh/archive/2012/12/05/creating-and-deploying-a-wcf-service-on-windows-azure-and-consuming-it-in-windows-8-store-app.aspx
With this one more specific to Azure Websites
- http://blogs.msdn.com/b/brunoterkaly/archive/2014/03/31/moving-a-wcf-service-and-database-to-the-cloud.aspx
HTH