I have a blog with .info extension which I want to switch to domain with .com extension. Is it good to do so?
If you do a 301 permanent redirect to the new URL then it should be fine. Whether or not it is "good" is a decision you have to make.
.com is one of the most recognized TLD's so you can redirect your domain as .com but for the country specific ranking is easy if you have chosen your country based extension.
Yes, it's good. If the .com domain is available for purchase, do it. You would just do a simple 301 redirect of all pages from your old .info domain to your new .com domain.
You should it if you've already had the .com domain before. Otherwise you need to buy .com if it's still available. .COM is always better than .INFO.
You can do this without any problem but make sure you must redirect your old pages with new one by 301 redirection. 301 is a permanent redirection to use.