The need to scratch items is a natural instinct in cats and should not be discouraged. To avoid your furniture being scratched you should have a sufficient sized scratch post for your cat/ kitten.
If they are scratching your sofa remove them and place them on the scratch post, if you keep doing this they will learn to use the scratch post.
When they use the scratch post, reward this behaviour as this will encourage this behaviour for the future.
Your cat/ kitten may use the scratch post naturally, others may need guidance. However they should pick this up quickly with the correct guidance.