Cannot upload demo xml file from premium theme

Hi

i bought a template from themeforest called Yellow Bird. The purchase also includes demo xml file so that i dont have to crack my head to start building the page from the scratch. The thing is, everytime i tried to import the xml file using WordPress importer, i got this message:

File is empty. Please upload something more substantial. This error could also be caused by uploads being disabled in your php.ini or by post_max_size being defined as smaller than upload_max_filesize in php.ini.

Can pls someone help me regarding this issue. it has been bothering me for a month already.

Btw, im using Plesk for my platform

thanks