UICollection View Adjust Cell Size for Screen Size
You can either use the UICollectionViewFlowLayout method itemSize property to set the UICollectionViewCell size, or use the delegate method, collectionView:layout:sizeForItemAtIndexPath: if you need to dynamically set the sizes of the UICollectionViewCells.
CollectionView layout Delegate that will help you to resize your Cell as you need.
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath;