Texture for iphone is not power of two?

Unity Engine
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1

Hi, every time i publish to my iphone
appear a text below of unity iphone saying that my texture is not power of two.

and if I select the textor inside unity appear this picture

how can I fix this please ?
thansk a lot !

note : i can use a lot photoshop,cinema 4D, but never hear about this.

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2

well 800x800 is not power of two (8, 16,32,64,128,256,512,1024)
Open it in a graphics application of your choice and either resize it to 512x512 or 1024x1024