I have other questions about merit, if I meet the required activity for Hero Member which is 480 activity. Do I need to gain 250 merits by default or I really need to receive it from someone who likes to give me merits by doing quality posts?
What if I do not get any merits until I got 480 activity so this will conclude that I will be stuck in my rank as senior member?
You definitely need another 250 merits to rank up even if you have 1000 activities. I don't know how you are going to make it but it is simple, keep writing quality posts here and some of them will get merited but not all. It's just the same as a whale upvoting your post on steemit.