Upgrading Drupal

I'm 30 days new to Drupal. I've studied the Drupal cookbook, auto installed 6.9 from Fantastico at Justhost.com web host, and upgraded to 6.10 per the directions that came with the upgrade.

After the upgrade to 6.10, when I install certain modules, I get the same red error message that I got before I upgraded, telling me about security issues and that I should upgrade. If I disable the module the error message goes away. The problem occurred with WYSIWYG API with FCKeditor, and with backup_mygrate. The problem did not occur with FCKeditor alone, without WYSIWYG API.

I am new on drupal i want to make a classified site. i want to display categories and subcategories on same page .Plz heip me how can i do it. I make a site like www.olx.com

My requirements are:

I'm in the middle of upgrading a 5.x installation to 6.10. Besides taking a lot of time I'm progressing very well :) But somewhere in the CCK, Image and FileField upgrade something went very wrong and my Image and FileFields went to inactive. I found a couple of posts about this problem and ending up enabling the fields again with:

I have to update from my Drupal 6.3 to a newer version - 6.10

But I have so many questions and worries! I don't want to ruin my website... Please tell me how safe that kind of update is, and is there any easy and safe way to update the core without losing much...?
I would really appreciate it.

I have a Drupal install that is long overdue to update. The update notifier gives me this list...
Drupal 6.5
Recommended version: 6.10 (2009-Feb-25)
Actualización de seguridad: 6.10 (2009-Feb-25)
Actualización de seguridad: 6.9 (2009-Ene-15)
Actualización de seguridad: 6.7 (2008-Dic-11)
Actualización de seguridad: 6.6 (2008-Oct-22)

Can I jump from 6.5 to 6.10 directly or do I have to install 6.6 & run update.php then 6.7, then 6.9 etc etc?

I was wondering, if I update my website for bugs and etc. Will I lose information on my site?