Upgrade site templates
A site template is a way to package site features and customizations that you can add to the solutions gallery for your own use. Site templates are often used to deploy solutions in a custom site or to provide site consistency within your organization. For example, you may have a standard policy on project management, and so you require the use of a custom project site template for all new projects.
If you want to continue to use site templates you created, then you must recreate them using the following procedure. Otherwise, all new sites created with those site templates will not work after you upgrade.
Follow these basic steps for each site template you have created in the solutions gallery.
Before you upgrade and while you are in 2010 mode, create a temporary site by using the 2010 site template. For more information, see Create a site.
When you are ready to upgrade and you have completed all other necessary preparations, upgrade your site collection to 2013 mode.
After your Office 365 subscription is upgraded, delete the 2010 site template from the solutions gallery.
Save the temporary site created in step one as the new 2013 site template. For more information, see Save, download, and upload a SharePoint 2013 site as a template.
If you want to continue to use the same site template, upload the new 2013 site template to the solution gallery of the target site collection.
Delete the temporary site. For more information, see Delete a site.
You can now use this 2013 site template to create new sites.