I want to convert all of the K2 items(Title alias, titles, full texts items, images, tags, description, keywords, users, comments, categories etc..). Is it possible to do that?
Yes it's possible, I've converted my Joomla K2 site to Wordpress a few days ago, first I found this Wordpress support topic http://wordpress.org/support/topic/need-to-convert-joomla-k2-website-to-wordpress , then asked gConverter guys to do it for me. That was well done.
I used cms2cms.com to convert my K2 to WordPress, cause it was supposed to ease working with Joomla, but in fact it wasn't easy at all, so I finally decided on WordPress. The procedure was quicker and way more simpler than I expected (and it's free).
You could use this free plugin for that: http://wordpress.org/extend/plugins/fg-joomla-to-wordpress/ - it also has a pro version with special features for "K2" - see plugin description there.
Thanks for mentioning, but at cms2cms I did precisely what the Premium ver does for free instead of having to pay almost 30 euro.
Do you really think an automatic tool such as cms2cms can do a clean conversion from Joomla site? Joomla sites are very complicated. Each Joomla site is unpredictable. I think this tool is very basic thing, because the migration script logic is one but differences of Joomla sites are thousands. I think such a tools are not right way to do a serous conversions.There are a few professional conversion services which will care about each bit of your Joomla site data. You can search those in google. Here are some of them: gConverter, GoWordpress, MigratetoWP.
I've used this automated service and it worked. You may read the tutorial and watch video on how to perform such migration http://www.squidoo.com/how-to-migrate-from-joomla-to-wordpress-with-cms2cms