Removing Border from gallery thumbnails

Hey All

I am fairly new to WordPress, but normally muddle my way through finding things out

but this has totally stumped me

I am using the DEEP FOCUS theme by elegant themes and all i wish to do is remove the border from the gallery and portfolio thumbs ….

I have tried altering the code in the css. sheet. Have tried replacing the image .pngs via ftp to replace the existing …. but nothing is working

Would really really appreciate anyones / everyones assistance on this

Also (but not as important) …. I have uploaded new coloured images for the hover / over image on the thumbs (called readmore-icon.png and zoom-icon.png) …. but these are still remaining as the themes white images …. Help here needed also ??

Beebs x