If u'r using Blogger Just Edit HTML code, then Find text "No follow" and change it with "Follow" But, If u'r Using WP, you can download Simple Plugins from here http://bloggertrick.com/wp-content/plugins/sem-dofollow.zip Good luck
actually if you are manually taking out the nofollow, you can just take out the whole rel="nofollow" phrase, no need to make it follow because it will follow anyway
If you use Wordpress, honestly I personally would suggest: http://www.michelem.org/wordpress-plugin-nofollow-free/ It has a lot more customizable options compared to the one listed above. - replace nofollow on author/text link ON/OFF - replace nofollow on registered author/text link ON/OFF - replace nofollow only if the visitor or the registered users had X previous comments - put back nofollow if blacklist words are matched - display number of comments by author - donate or not a link to nofollow free plugin - Image band ON/OFF - Position Right/Left - Colors Green/Red/Orange/blue (see the image below) - Url to link it to It has a lot of options built in to fully customize the dofollow feature. If you just want to turn it on/off either plugin would work, If you want to have more features available now or down the line this is what I'd recommend.
If you want to attract people to your blog with the comments. Consider adding the Keywordluv and/or commentluv plugins. Then submit your blog to dofollow search sites.