Spells and ranged Attacks can be non-lethal, you must declare that the attack is non-lethal before you make the attack roll or before the save is rolled, saying it afterwards does not count. Be sure to communicate your intent. However the DM also isn't going to be bitch about it, but when the DM asks and you state your intent, you cannot change it afterwards.

However there are some restrictions:

• 3rd-level spells or higher that cause an AOE effect cannot be non-lethal.

• 5th-level spells or higher can never be non-lethal.

• Up-casted spells follow the same rules.

Some unique exceptions exist, spell such as Disintegrate can obviously never be non-lethal, duh.