When you are logged in to your blog, on top you see a sidebar.
Click customize -> widgets
There you'll see all the widgets on your blog.
Click on the red cross to the right to delete.
Or click on add widget to add some.

Hope it helps :)

Hello,

Thanks for your help.

Actually I did search some posts before and noticed that this may be done through the customize -> widgets page. I tried to edit all the widgets settings one by one, however it seemed that none of them are linked to "Home", "About this system", "About Blog A", "Contact".

Here's what I tried the links in the customize -> widgets page.

Header
* Blog B Title (Blog title)
* Tagline for Blog B (Blog tagline)

Menu
* Blog home link (Menu link)
* Pages (Simple Page list)
* Blog owner contact form link (Menu link)
* Log in form link (Menu link)

Page Top
* All blogs (Public blog list)

Sidebar
* Calendar Widget (Plugin)
* Blog B Title (Blog title)
* Long Description of this Blog
* Common Navigation Links
* Search (Search Form)
* Categories (Category list)
* Linkblog (Simple Linkblog Links list)
* XML Feeds (XML Feeds (RSS / Atom))

Sidebar 2
* Contents (Simple Post list)
* Recent comments (Comment list)
* Recent photos (Photo index)
* Sidebar 2 (Free HTML)

Best regards

Alex

Menu
* Blog home link (Menu link)
* Pages (Simple Page list)
* Blog owner contact form link (Menu link)
* Log in form link (Menu link)

That's the ones ;)

¥

should have mentioned that...mea culpa :)