In my opinion, you *should* be using the largest size possible. Storage space is CHEAP, and it's way easier to take a really large, high-res photo and crop it to end up with something decent, than it is to take a medium or small file, low-res photo and do anything with it. Keep the large file size!
Your bird photos: If *all* you want to do is snap pics that identify the bird and post them on FB, then you've done that. But if you want to go beyond that at all, you've got some work ahead of you. Bird photography is TOUGH, and honestly, I'm not sure I'd recommend starting there. I'd start with things that don't move so fast.
If you don't want to shoot manual, does your camera have a shutter-priority mode? Set your shutter speed pretty high, then change your aperture and ISO until your exposure is good (meter on the bird so it'll be exposed correctly, even if the background blows out a little). I know nothing about your camera, so I don't know how high you can go on the ISO and still get decent images...but I generally start with a shutter speed of at least 1/1000. Aperture setting around 8, but I might go wide open if I have to for exposure purposes, and ISO...I start at 400 and go up until the exposure's right.
The higher shutter speed will help a little with the blur, but you also need to make sure you try to get the focus on the eyes. Does your camera allow for single-point focus? If so, use that and aim straight at the eyes.
Some other things you can do to improve:
--Get closer. We bird photographers use a lot of methods to do that (some more reasonable than others, lol) but if you'll just wear neutral colors (brown, black, dark green), find a good spot and sit or stand still, the birds will come to you, especially song birds. I set out feeders, next to natural habitat. Then I try to catch the birds "staged" on the natural elements near the feeder.
--Watch your composition. In all of these except the last one, your subject is placed smack in the middle of the frame. There's nothing compelling about the composition that draws the eye. Just about the only time I center my bird photos is if the bird pretty much fills the frame.
In the last photo, the bird isn't centered, but the bird is over on the left, LOOKING left and it draws the eye right out of the frame. The entire right side of the picture is useless, because the eye is going to focus on the bird, then follow the direction the bird is looking, to the left. I realize that you can't just ask the bird to turn and look the other way (though God knows, I've tried!!), so you have to try to compose differently. In this instance, I would either have taken the shot to allow more room on the left in the direction the heron is looking, or cropped in post to eliminate most of the right part of the picture.
--Lighting. Best way to get decent lighting on birds? Make sure that you are between the sun and the birds. Situate yourself so that the sun is behind you, then shoot in front of you toward the birds. You'll get better exposures, better catchlights, and the birds will just stand out better.
There's only so much you'll be able to do with that camera, in terms of bird photography. But there IS definitely room for improvement, if you're interested in working on it!! Keep shooting and keep posting!
(And lest that all sound like I'm bashing: these are better than most of MY first bird pictures...)