Thanks a lot for your reply! You are right, I didn′t know about the differences between WP.COM and WP.ORG. I have a hosting for doodledatabaze.cz domain, so I am able to use WP.ORG. But recenetly I have created my blog on WP.COM and mapped the domain doodledatabaze.cz. Now I want to switch from WP.COM to WP.ORG, but I can not run installation. If I am right, it is not possible to run WP.ORG publishing system on the domain, that is mapped on WP.COM? I have tried to set the nameservers for my domain back from wordpress.com to my hosting, but it does not help, I still can not run istallation of WP.ORG. I think it is because the mapped domain is still pointing to wordpress.com servers, no to my hosting servers.
I am not sure how to solve this problem. Should I unmap my doodledatabaze.cz domain? An if so, how can I unmap it?