Requests are against the rules. You should stop before you get an infraction.
You're saving the sprites as JPEG, which is very bad because JPEG is inherently lossy. Lossy formats are never good for pixel art. From now on, save as GIF or PNG instead because they're not lossy.
Revamps are more than simple recolors, so you should label these as "recolors" instead.
If you're aiming for D/P sprites, you have to resize the sprites to 80x80 pixels and adjust for anatomical correctness. For example, the fourth generation Articuno has a grey beak and all of its counterparts in earlier generations have bluish-grey. Also, look at the difference in body between the first and fourth generation Venusaur:
This is my first sprite criticism, so here goes nothing.
This one could use more layers of shading. Also, judging from the levels of shading that you use, the light comes from the bottom. The sprite would look better if the light source was from the top or front.
This is actually your best one. Again, the shading looks awkward. You should also use a lighter pink on the body.
Honestly, this is an eyesore. You tried to contrast with solid red and green, which is a huge mistake. If you do color complements, you have to make the colors more diluted. For example, use light red-orange and washed out green. Look at this D/P sprite.
You're using ugly shades of green and the colors are too dull. This is one of the few situations where I would recommend using several shades of lime green. If you're trying to make this D/P-ish, it looks like it follows the overworld Sinnoh tileset color scheme. The sprites themselves don't look anywhere near as dull.
Shading again. Also, this sprite is not anatomically correct so it shouldn't be used at all. No matter how well you revamp it, it'll still be like the Green version of Venusaur.
This one actually isn't that bad. It needs lighter colors and a little bit of gloss to its exoskeleton.
This one's too cartoonic. Shading and using more blended colors would solve this.
Overall, these sprites are terrible. You shouldn't do requests for anybody until you get better at doing this. Or at least know what's the difference between a revamp and a simple recolor.
It would also help to do constant side-by-side comparisons between the sprite you're trying to revamp and the D/P (or whatever style) sprite you're trying to imitate.
Again, this is my first time doing a detailed criticism so don't take all the things I say seriously.