yes u can, in fact u should... normally i reroll immediately if i get 40g. if still same, i just leave it there till next day.
btw, just now i think i kena lightning storm by a real shaman... was playing half way in arena and suddenly kaboom! my house short circuit black out after this lightning.....   gg arena....putih putih lose...

cos u can farm the gold faster...

instead of 40 gold, u will have a change to get 60 or 100 gold.

i was worried that the quest will gone after i press the 'x' 

exactly... u wanna get 40g per day, or 60/100g per day? the choice is obvious right?

so, everyday u can reroll the daily quest once if u do not like it. take advantage of this to try and get a better pay daily quest. then use the gold to buy packs if u r new to this game, or arena for better worth if u have more experience.

http://hearthstone.gamepedia.com/Quest

Completing the one time "Unique quests"(also call hidden quest)

when you have more then 2 same cards, Dischant the 3rd for "Crafting Time" quest (Disenchant a card: Earn 95 arcane dust) because you deck only allow maximun 2 indentical card, since you can't use it anyway
in my begining days, i made a mistake thinking DE a blue(which i though it was useless at the time) and get the dust to craft another blue(which i deem useful) is a good trade. wrong, (but i was desperate for a good card), now that blue card is let to rot in my collection

i assume you have clear all classes(vs AI) with your mage/paladin to unlock all 9 classes,
if you are going for expert mode for Crush Them All! quest(Defeat every Expert AI Hero: reward 100 gold)
i suggest you do it in a sequence, so you won't forget which hero you haven't defeat.

my advice for beginner is "Legendary cards doesn't win game (but it help alot)"
in my early days, i always fear legendary cards for i have none, heck i don't even have epic card, but i learn to play smart. and when i win, it feel awesome.

hearthstone on iphone? let's wait until 9 sept and see
http://www.reddit.com/r/hearthstone/commen...at_apple_event/