What size ( height and width) and file type does the logo file need to be to show properly? My jpg keeps getting cutoff on the top and bottom for various sizes of files

Hello Tracey ! 
At the moment Our DW Focus uses the logo size of 230 x 80 px. For example,if you want to change size for the logo to450 x 70 px, you can do as the following: 
Step1: Log in to Dashboard > Appearance > Widgets > Header, Delete all the Text widgets in the Header section. 
Step 2: Go to Dashboard  > Appearance >  Customize > General Settings, add the following code to the Header Code:

<style>
 .site-header #header {
    background: none;
}

#branding {
    width: 450px !important;
}

.site-header #branding a {
    width: 450px;
    height: 70px;
}
</style> 

Step 3: Log in to Dashboard > Appearance > Customize >Select Title & Tagline, then upload the logo with the size 450x70px
Notice: You can re-size in the line code to match with your logo. Hope this helps !