After the long step by step how to use PicMonkey to create a banner I didn't have the heart to add this on the end as it was already a very long post!
This is pretty straightforward. Go to PicMonkey and click on collage.
You will be asked to upload a photo. Upload your current blog banner.
The image above has the layout option shown second down on the left, the three blocks. Click on this, select FB Cover. There are several layouts, I use the one of the left with the fewest blocks.
Go back to the photo you just uploaded, which is found in the top menu on the left with the landscape image option. Drag the image over into the largest box.
Each of the two empty boxes will have a cross in the top right corner, click on this to remove the box.
This should leave you with the perfect sized banner to upload to Facebook so you can use the same banner on your blog and Facebook.
At a glance this may seem like a lot of steps when you could just resize an image, but PicMonkey does this for me without any trial and error getting the sizes right and only takes a couple of minutes.
I tend to update the photos on my banner each month with my favourite photos, following the steps in this post and my previous post to update my headers on Blogger and Facebook now only takes a matter of minutes since I already did the hardwork to create the blank template (as mentioned in my previous post.)
Hope this helps - any questions please ask, I'm no technical expert, but I am familiar with what I do!