I'm owning a web site of more of 2500 pages, with totally more of 5000 adsense ads placed by hand. It look impossible to me to change more of 5000 ads code by hand, how I could change the owner in an automatic replace way?
Look for a software that will search and replace text in multiple files, i.e. mass search and replace. There used to be a software like that I used in late 90s when HTML and PERL was the most popular means of creating web sites.
are you the new owner of the site? site this large should have PHP include or SSI (server side include) setup for common files. look at the source code and see if you can find any reference to "include" you will be lucky you you have it. all you need to do is to update one file and opload, all pages are fixed. but if this is your site and thats the way you did it, then i would have to say that wasn't a very wise thing to design a site like that. try to find a tool, see if you get lucky