Dear, to remove the recorded voice follow these easy steps:
Open the power point file having the recorded voice.
Click on the "Slide Show" and then " Record Slide Show"
Then you will find "Clear" option in sub menu.
Click on the "Clear" and then "Clear Narrations on all slides".
This will clear all voice from all slides and if you want to clear from the current slide then click on respective option. Similarly, you may clear Timings from your slides.