Quinton led the Iron to the National League after his first season in charge but leaves the club at the foot of the table after just one win all season.
Their most recent defeat came yesterday as they lost 2-1 at home to Eastleigh.
A statement on the club's website reads:
"A sad day for the Club, but we felt it was time for a change. Brad has done well for us as both a player and manager - being involved in three promotions in eleven years - we thank him for his contribution, he knows he will always be welcome at Cressing Road.
"We feel we backed Brad as best we could, even allowing him to bring in another new player on Friday. The Board has never interfered in the manager's selection of players, but we must operate within our means.
"Even as late as the last twenty minutes on Saturday, I was hoping that we would be able to turn our season around and give ourselves a chance. Yes, the Club could have continued down the path we have for the first fifteen matches, but we were not confident that we would turn our season around. Time will tell if a change brings an improvement in our fortunes, but we felt we at least have to try."
"Looking ahead, the Club will appoint a caretaker-manager over the next few days and will be having a pre-match meeting with the staff and players at 6.15 on Tuesday evening prior to our County Cup game with Canvey. The Club will advertise for a replacement and will take time in assessing the best candidate for the journey ahead.
"What the Board are looking for is someone to work with us as we strive to consolidate at this level once again and be part of our ambitious plans for the future."