Changing your seat location is based on your tenure as a STH. I got my seats 6 years ago and since I wanted 4 together I had to sit in the old 222 section for a year and then relocate to the $300,s where I originally wanted(ironically my seats in 222 which were terrible costs more than what I am paying today for my seats in the upper bowl). I was told that after that first season I would have a chance to relocate to the 300,s based on seniority. I believe the next season first timers were able to get 300,s as STH,s.
It might be a little tougher today if say you sign up for seasons at $155 and want to downgrade to $50 seats after one season but it is all based on seniority. I never hear anyone saying that they want to change their $50 seats for $155 seats which speaks volumes about the way the pricing of the lower bowl is all out of whack.
You do not have to cancel your subscription and start over but you might get stuck in your seats again as there is no guarantee to relocate just that if anything is available you can move based on seniority.