Macro to automatically update Word styles to new template

We want to develop a macro that can change the styles of our old documents to match the new template. Our old documents have 20 styles (1 to 20), while our new template has 10 styles (1 to 10). Currently, when we try to update our old documents to the new template, it takes styles 1-10 from the new template and styles 11-20 from the old template. We want to change this so it uses styles only from the new template. I want a macro that will follow the following logic If there are 10 styles in template and 20 styles in document Change document style #1 to template style #1 Change document style #2 to template style #2 Change document style #3 to template style #3 Change document style #4 to template style #4 Change document style #5 to template style #5 Change document style #6 to template style #6 Change document style #7 to template style #7 Change document style #8 to template style #8 Change document style #9 to template style #9 Change document style #10 to template style #10 Change document style #11 to template style #1 Change document style #12 to template style #2 And so on By using options>addins>templates, i can change the first 10 styles easily But I also want to change the remaining document styles 11 to 20, to the styles 1 to 10