The recommended image sizes are
Post featured image ( With sidebar)
Width: 750px;
Height: 400px;
Aspect ratio:15:8
Post Feature Image (Without Sidebar)
Width: 1140px
Height: 500px
Aspect Ratio: 57:25
Slider Image
Width: 1920px
Height: 650px
Aspect ratio: 96:25
Page featured image ( with sidebar)
Width: 750px;
Height: 400px;
Aspect ratio:15:8
Logo:
Width:182px;
Height:82px;
Ratio:91:41