MySQL add days to a date
UPDATE classes
SET
date = date + 1
where id = 161

SELECT DATE_ADD(`your_field_name`, INTERVAL 2 DAY);

UPDATE classes
SET `date` = DATE_ADD(`date` , INTERVAL 2 DAY);
WHERE `id` = 161

UPDATE table SET nameofdatefield = ADDDATE(nameofdatefield, 2) WHERE ...

update tablename set coldate=DATE_ADD(coldate, INTERVAL 2 DAY)

SELECT DATE_ADD(CURDATE(), INTERVAL 2 DAY)

UPDATE classes
SET `date` = DATE_ADD(`date`, INTERVAL 2 DAY)
WHERE id = 161

DATE_ADD(FROM_DATE_HERE, INTERVAL INTERVAL_TIME_HERE DAY)

DATE_ADD(NOW(), INTERVAL -1 DAY) for deducting 1 DAY from current Day
DATE_ADD(NOW(), INTERVAL 2 DAY)  for adding 2 Days

UPDATE classes WHERE date=(DATE_ADD(date, INTERVAL 1 DAY)) WHERE id=161

SET date = DATE_ADD( fieldname, INTERVAL 2 DAY )