Quoted from Jamwin:
According to JJP tech support, you can do the WIFI update from v1.34 to 1.37. Once you update to 1.37, the update will work via wifi. To get to 1.37 from v.1.34 you have to do it via USB. I have been trying to update it via the delta1.34 to 1.37 USB and keep getting "fail to update". Spent some time yesterday communicating with JJP tech support, which was prompt and helpful, but ultimately going to have to do a full update to get to 1.37. Didn't have time to do it yesterday so will do it this weekend. Hope this helps.
Forgot to add, I had the same issue when trying to do it via wifi and was stuck on the screenshot you provided for over an hour and didn't do anything, which prompted me to reach out to JJP Tech support.