Voice fixer 8000hz to 16000hz how to upsample wav to 16000 hz using voice fixer

[PHVK1611]

every time when i try telephonic wav(8khz) to rise it to 44khz it removes clarity of audio.... how to give custom upsample rate and there Are 2 people voices in my wav file but when i upsample with voice fixer ,the output wav has only one person voice