cocos2d change sprite texture-Collection of common programming errors

I want to change a sprite texture with another texture from a sprite sheet

//normal sprite
character = [CCSprite spriteWithSpriteFrameName:@"char1.png"];

//change texture
[character setTexture:[[CCTextureCache sharedTextureCache] addImage:[CCSprite spriteWithSpriteFrameName:@"char2.png"]]];

but this gives me an error.I have tried without spriteWithSpriteFrameName and it gives me a blank texture.

//error
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[CCSprite lastPathComponent]: unrecognized selector sent to instance 0xab32580'

please help me to solve this problem