My current XF version is 2.1.4, So How do I upgrade to the latest version properly. And Another question is how opten I should upgrade? Should I upgrade every updates Xf releases ?
That's what I do unless it's a major update that breaks addons.
You should be able to upgrade directly from the admin panel from 2.1.4 to 2.1.7. It's just bug fixes. If your forum has over 1 million posts, you might want to do the upgrade from the command line.
My site just started so nothing to break right now. But I need to learn to handle these things asap. So major updates do break plugins you say? I looking for most stable situation for my site and using just the default theme without any plugin.
They can, so you need to check the addon's page in the resource manager to check in with the developer to see if it works fine. Or you can set up a test forum and test things out for yourself before upgrading your live site.