Search and Replace a a partial string / substring in mssql tables

I was tasked with moving an installation of Orchard CMS to a different server and domain. All the content (page content, menu structure, links, etc.) is stored in an MSSQL database. The good part: When moving the physical files of the Orchard installation to the new server, the database will stay the same, no need to migrate it. The bad thing: There are lots and lots of absolute URLs scattered all over the pages and menus.

I have isolated / pinned down the tables and fields in which the URLs occur, but I lack the (MS)SQL experience/knowledge to do a "search - replace". So I come here for help (I have tried exporting the tables to .sql files, doing a search-replace in a text editor, and then re-importing the .sql files to the database, but ran into several syntax errors... so i need to do this the "SQL way").

To give an example:

The table Common_BodyPartRecord has the field Text of type ntext that contains HTML content. I need to find every occurance of the partial string /oldserver.com/foo/ and replace it with /newserver.org/bar/. There can be multiple occurances of the pattern within the same table entry.

(In total I have 5 patterns that will need replacing, all partial string / substrings of urls, domains/paths, etc.)

I usually do frontend stuff and came to this assignment by chance. I have used MySQL back in the day I was playing around with PHP related stuff, but never got past eh basics of SQL - it would be helpful if you could keep your explainations more or less newbie-friendly.

The SQL server version is SQL Server 9.0.4053, I have access to the database via the Microsoft SQL Server Management Studio 12

Any help is highly appreciated!