How much weight should I lose?

So, I'm obviously overweight. In your opinion, how much weight should I try to lose? I'm going to do it the healthy way, with diet and exercise. Here are some pictures of me for reference:
38.media.tumblr.com/.../...8fDDBL1ref7sqo1_500.jpg

38.media.tumblr.com/.../...glW2Rl1ref7sqo1_500.jpg

31.media.tumblr.com/.../...9je3v01ref7sqo1_500.jpg
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+1 y
I'm 5'3 by the way
How much weight should I lose?
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