If I cancel, will it keep me active till the end of the purchased period? Thanks!
AFAIK, your subscription remains active until the end date has expired; so you could cancel immediately and still have access until the end of the month/year (as appropriate). Although, I have never cancelled my subscription...
If you update your plan with the coupon, you will be billed as of today, but you will receive a pro-rated credit for the unused time.
For example, if you are a monthly subscriber and you have a couple weeks until your usual renewal date, you'll be credited $4.50 and then charged the yearly discounted amount.
So, don't worry about your renewal period - there is no need to cancel, and you'll be refunded the remaining unused time.
@wilburpowery as you see @webspilka response above, it seems he has renewal at discounted rate.
Besides that, I also had a subscription at discounted rate 2 years ago and renewal came at same price, although for some reason I wasn't able to continue.