I have installed ERPNext v11.1.16 in our testing server.
When I was setting letter head, I inserted the logo in the content editor box. When I clicked on the logo it is not allowing me to resize it. In earlier versions resize option was available.
I have been running v10 for about a year now and I was never able to resize my logo’s in ERPNext so I downloaded the free versions of IrfanView because it has a very simple interface for resizing my logos.
I was not aware that you could now resize them in v11.
While you are waiting for it to get fixed, you can use the program I linked above.