Fixing Header/Logo Size

Hi, I am very new to blogging and wordpress and my logo is way too small. I tried writing a code I found in one of these forums into my child theme but it did not work. Can someone please help.

website:
https://www.theedgeofchic.com

current logo size is 400 x 117 and in jpg form. does that matter?

I tried a couple codes but neither worked. Here is the one if have now that is not working. maybe I have to edit the code more, I am just copying and pasting what I found.

/*increase or decrease the logo size*/
.brand.span3{
Width:23%
}

Thank you!