"These aircraft will allow us to carry more customers, particularly at peak times, to holiday destinations."
The change sees the number of seats increase to 186, up from 180. Jetstar estimates that will equate to an extra 600,000 passengers every year, without adding a single flight.
The low-cost carrier has also promised that leg room or seat width hasn't changed with the addition of six extra seats. The average seat pitch on Jetstar is 29 inches (73.66 centimetres).
The refit comes after Jetstar was ranked as the worst airline in the world, according to a global consumer survey released by Choice in April year.
Choice and 10 other consumer groups surveyed 11,000 passengers from Australia, Belgium, Brazil, Denmark, France, Italy, Portugal and Spain.
Jetstar came in last in the customer satisfaction survey, which rated airlines on their check-in and boarding processes as well as their meals, punctuality and cleanliness
"This is yet more evidence that Jetstar needs to clean up its act. It's one thing to be low cost but quite another to be low rent," Tom Godfrey, Choice's head of media said of the results.
"It's not too surprising Jetstar rated so poorly given its track record of delays and cancellations and its policy of landing its customers with sneaky pre-ticked extras."
However, Jetstar quickly hit back at the survey, claiming it has no credibility.
Jetstar spokesman Luke Enright criticised how the research was conducted and said it was not a fair indicator of all airlines.
He said the data size of Jetstar passengers which included more than 100 respondents of the 11,000 overall was "around half the number of people we carry on one flight and a lot less than 34 million customers who flew with us last year.
"They also called it an international survey but only surveyed people from eight countries."