and found no helping hint. .htaccess modifiing dont work, disabling compression modules dont work....so please help.

Hello Everyone, i got a question: i cannot upload large files with 2,5 GByte in Size. 1,5 Gbyte work fine but not much more. Caching Modules have been disabled in Apache2, .htaccess is provided as in xupload_pro zipfile that came after purchasing. Our aim is it to allow uploads with 5 Gbyte in size....