Select the INCORRECTLY spelt word.

The correct answer is Tution.

Let us analyze the spelling of each of the given options to identify the incorrectly spelt word:
1. Tution: This spelling is incorrect. The correct spelling is Tuition (which includes an 'i' after the 't'). Tuition refers to teaching or instruction, especially of individual pupils or small groups.
2. Circuit: This spelling is correct. A circuit is a circular journey or a complete path around which an electric current can flow.
3. Genuine: This spelling is correct. Genuine means truly what something is said to be; authentic or sincere.
4. Manners: This spelling is correct. Manners refers to polite or well-bred social behavior.

Therefore, the incorrectly spelt word is "Tution".