Jim I use to use "resizer" on my phone. I tried the "resize it" app first but was never successful. Just get the app and follow the instructions. The real key is reducing the picture to the accepted size not exceeding the maximum. A little below maximum worked for me.
However I have a new set up and have not set the phone up for posting pictures. Maybe others will have other options, chiming in to you aid.
The15thMember post here from her computer. I feel certain she will be able to help you with the computer part as others as well.