With the new release of facebook ios sdk, the documentation is talking about the facebook like control, that allows to like a page. https://developers.facebook.com/docs/ios/like
You can not change the size of button because its standard button provided by fb but you can use button style using below code:
Here is the complete code:
[FBSettings enableBetaFeature:FBBetaFeaturesLikeButton];
[FBSettings enablePlatformCompatibility:NO];
FBLikeControl *like = [[FBLikeControl alloc] init];
like.objectID = @"http://shareitexampleapp.parseapp.com/photo1/";
like.likeControlHorizontalAlignment=FBLikeControlHorizontalAlignmentRight;
like.likeControlStyle=FBLikeControlStyleBoxCount;
[self.view addSubview like];