Upgrading Drupal

At the moment I have a friend who bought a site. The site came with drupal and vbulletin integrated. http://www.talkhomebusiness.com
Is it possible to upgrade without losing any of the articles, blogs etc?
Will the upgrade wreck the current style?
Any steps on how to do this?

Help or info would be great.

Thanks
Demon

I've updated my 4.7.3 website to 4.7.4 and now I can't login. I don't get any error, the page just reloads but without loging in.
HELP

I know it has been asked before, but so far I haven't been able to find a helpful answer. Therefore this question again: when upgrading from 4.7.0 to 4.7.4 (running from preselected version 180) I got these warnings:

Hi,

I ported Drupal to a new URL. Now the user login dialog http://example.org/?q=user is screwed up.

After I login or logout I am pointed to pages to the old URL. I checked the database and found URL entries in the table "sessions". I assume that this old data does distort the function of the login at the new site.

Is is possible that Drupal takes the URL where is will point to after the login and the logout aout of this table?

I am in over my head! I am a director for an Indiana based non profit. We decided to migrate our site to a drupal based setup. My problem is that our web person split, and I am now left to clean up the mess. In trying to install a new theme, I get many egregious mysql errors. They are visible when browsing to the site. : http://www.inspireindiana.org

Any help would be much appreciated!

I have just updated from 4.5 to 4.7 (w/o 4.6 in between). There were several errors, all of which have been resolved. The remaining problem is that when someone clicks on login they are directed to http://user/login. Obviously, this should be http://www.example.com/user/login.

Any suggestions?