I hope that you understand that changing the URL means that every original link in the original blog will be broken. If your posts and pages have already been indexed by search engines then when the original URLs are clicked the result will be 404 - page not found. It will take 3 - 6 months before any indexed items are removed from Google's cache. As well as that the content with the new URLs will have to re-indexed by search engines. If your content has not yet been indexed by search engines this is not a problem. But if it has been you would be wise to know what will happen and that's why I have posted. Others did not understand this and regretted the change they made.