Google analytics tracking codes

[Anaksagorija]

Hello everyone. recently i have encounteda problem with Google analytics. it happened that my ex partners have cancelled me an access to admin system of my sites so now I can only watch the results obtained. and I am planning to settle new accounts for my sites but at the same time I do not want to lose the data that I am getting currently. the problem now arises that to settle new accounts I have to install tracking codes and to delete the old ones. but if i delete them i will lose all the data.
does anyone know what will happen if there are 2 tracking codes on the site?

the system reports the following note:
We recommend that you do not include both tracking code snippets together on any given page. Doing so might generate inaccurate report data. You can, however, migrate select pages of your site to the new tracking code while the legacy code remains on others.

does it mean that i have to delete the old code for some pages and to add there a new one?
Will be greatful if anyone replies me or gives a hint where i can get the answers. thank you