you could try an update on the contents table directly through phpMyAdmin using the replace function:
http://dev.mysql.com/doc/refman/5.5/en/string-functions.html#function_replace
the syntax would look like:
UPDATE pcms2_contents SET ContentValue = REPLACE(ContentValue,'/antronix/','/') WHERE ContentValue LIKE '%/antronix/%'
I Would strongly sugest backing up the table first.