Help with upgrading and plugins after a year break.

Hello, I’m an illustrator using wordpress to run his website. I took almost an year break from my website and today i wanted to start posting new works on wordpress.
I saw i had to upgrade to 3.0.4 while I was still with 2.9.1
The problems I encountered were the following:

Automatic upgrade failed with this error: Could not copy file: /public_html/wp/wp-content/upgrade/wordpress-3.tmp/wordpress/wp-trackback.php

I tried to upgrade manually, but when i upload the wp folder, cyberduck is telling me he can’t replace some files, it says i don’t have the permission (but i have it, i’m the only administrator of my host)

Then i tried to erase some old plugins (nextgen gallery) that i didn’t want anymore, and this was the error: Plugin could not be deleted due to an error: Could not fully remove the plugin(s) nextgen-gallery/nggallery.php

I tried to manually erase the folder but it won’t let me, permission problem.

I have all my files set to 755, being administrator I don’t see why I can’t delete stuff from my wp folder!

What should I do? Please help!

Thanks in advance.

Nick