Generally, where a member of a class (the class of all universities) is particularised (say by the addition of "Wroclaw") then you don't need the definite article.
Wroclaw Polytechnic or
Wroclaw University of Technology
will be sufficient for a letterhead. Some insititutions do require the The, but that's a matter of style/affectation which they have adopted.
Where the name of the institution has the determiner/particulariser at the end (as in "University of Sussex") it's normal to use the definite article at the front because there is only one of that particular institution.
The University of Sussex
This applies to including the name in other sentences, too:
I attend the University of Sussex.
I attend Sussex University.