1. If a hero gains a new resource icon, does he still have the former resource icon? (Same case to characters trait)

If not, can i discard the attachment whenever i want? (Is there such an option to discard an attachment?)

2. Each turn we have more than 3 resources income while we can only get 1 card from the pile, which leads to a lot of unused resource tokens in heroes resource pool. How can i handle this situation?

1. they keep the old one

2. if anything you dont get enough- remember that most cards cost more than 1 resource, the average being 2 cost, and theres alot of 3 cost cards, so most of the time you are saving

if you have too much there are cards such as aragorn and longbeard map maker who can spend them to do actions

rich

And no, you can't discard attachments unless a card effect tells you to do so.