AutoSizable Swift 2 - swift

Question

This is a part of GameScene.swift.
I want to make Background and Lives auto sizable. This is the code that works only for iPad. I want that it can work on iPhone and I don't know how to do, because of the function createLives.
import SpriteKit
import AVFoundation
class GameScene: SKScene {
var scoreLabel: SKLabelNode!
var score: Int = 0 {
didSet {
scoreLabel.text = "Score: \(score)"
}
}
var livesImages = [SKSpriteNode]()
var lives = 3
var activeSliceBG: SKShapeNode!
var activeSliceFG: SKShapeNode!
var activeSlicePoints = [CGPoint]()
var swooshSoundActive = false
override func didMoveToView(view: SKView) {
let background = SKSpriteNode(imageNamed:"sliceBackground")
background.position = CGPoint(x: 512, y: 384)
background.blendMode = .Replace
background.zPosition = -10
addChild(background)
physicsWorld.gravity = CGVector(dx: 0, dy: -6)
physicsWorld.speed = 0.85
createScore()
createLives()
createSlices()
}
func createScore(){
scoreLabel = SKLabelNode(fontNamed: "Chalkduster")
scoreLabel.text = "Score: 0"
scoreLabel.horizontalAlignmentMode = .Left
scoreLabel.fontSize = 48
addChild(scoreLabel)
}
func createLives() {
for i in 0 ..< 3 {
let spriteNode = SKSpriteNode(imageNamed: "sliceLife")
spriteNode.position = CGPoint(x: CGFloat(834 + (i * 70)), y: 720)
addChild(spriteNode)
livesImages.append(spriteNode)
}
}