Beginning in version 4.8, you can convert a template to a different key indicator.
While in your template, select the 'Mapping' dropdown at the top. Then choose 'Convert'. Select the option that is appropriate for your need.
Once you have converted your template, you will need to review your mappings to ensure that all required fields have been satisfied as fields in your constituent mapping will have changed due to the conversion. You may also need to change other areas of your template as your data needs require.
You can watch a brief video demonstration here.
If you are working with a combined file, you may find this knowledgebase article helpful.