Captivate 9 - how to change background slides to jpeg or png from .bmp

Hi, can anyone help? 

I've recorded a web based system as a system simulation 

it has created a ton of slides

background slides are huge and our LMS team are saying they are .bmp files which need to be converted to jpeg or png to reduce the file size..

they are showing as 3686.41 each only 1 usage 

How do I do this? and how do i do this when i record in future.. this is ongoing project 

thanks Hazel