Some time ago I have lauched my personal site as a blog, which became quite popular and also has a good SEO index (for instance in Google there are indexed all the blog articles). At the launching time I didn't thought much about its usage, but now I want to make some changes, the most important being moving the blog from the main domain to a subdomain. What is the best way to do it in order to not waste all the SEO efforts so far?