Almost triple file size when updating theme

[caz46]

Hi,

I have PPT2013 templates with existing themes. I have been given some .png files to change the background image in the Slide master.

Using the Format background option, I select File and then update the image.

However, this drastically increases the file size, from 3,070KB to 8,083KB.

I am wondering if this method just adds the new background image on top of the old one instead of replacing it?



I have tried to find a way of deleting the background image without all the other theme settings i.e. font styles etc but cannot find anything.

I need to update these templates quite urgently, so if anyone has any ideas or advice, I would love to hear them.

Thanks in advance.
Caz