Finally, the OP could donate 50 BTC to the forum and become a VIP. VIPs have the ability to change their usernames at will.
isnt 50BTC is too much for newbie just to change his name if he can create new account and easily get back his activity points?
In 99.99% of cases, sure. But the OP could be an early adopter with thousands of coins. Lots of people have spent more money than 50 BTC on weirder things and besides, a donation would benefit the forum. I agree it's pretty unlikely though which is why I only briefly mentioned it at the end of my post.
even OP is an early adopter i dont think it is reasonable to pay thousand dollars just to change the name of a Newbie account..
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i recommend you to use that account until it became atleast Member or Full Member.. tomorrow you will have a maximum of 42 activity points ( Jr Member) if you do some post 
If we measure using UTC time, then it should change today provided the OP makes enough posts. However, becoming a member requires 60 posts and becoming a full member requires 120 posts and (usually) waiting several months so it's possible that the OP might not want to wait so long.
OP will wait much longer if he will create new account, it will be 3 2-week period behind his current account
so i suggest OP to just ignore his username and continue contributing good things to this forum