Question

how can we remove unwanted part of an image in PowerPoint

Answer 1

just crop the image if possible or first edit the image in pshop and then insert.
:)

Answer 2

Click the picture that you want to remove the background from.

Under Picture Tools, on the Format tab, in the Adjust group, click Remove Background. ...

If necessary, under Picture Tools, on the Background Removal tab, do one or both of the following:

I hope it can help you.....