How to keep Assets when publishing Game

I have made a game that works perfectly fine in the unity dev software but when i publish to web form or android i lose the ability to show my assets. I know i should of used a prefab but this is the route i took so could you help me with this route. I decleared my vars like this

sfxHit = Resources.LoadAssetAtPath("Assets/heavenly_choir.wav", AudioClip);
splatsound = Resources.LoadAssetAtPath("Assets/Splat.mp3", AudioClip);
oldSprite = Resources.LoadAssetAtPath("Assets/dog-1.png", Sprite);
newSprite = Resources.LoadAssetAtPath("Assets/dog with parachute.png", Sprite);

What i need is to be able to access the images and audioclips when i publish the game to other platforms.

GetComponent(SpriteRenderer).sprite = oldSprite;

This is what i am using to change the sprite.

Resources.LoadAssetAtPath() is for Editor use. To solve your problem, put your content into Assets/Resources, then use Resources.Load() to pull the assets in.