As pointed out, if I also recall correctly, you cannot change the currency for an account.
You don't need to. You can advertise in US. Your bids will be in Turkish currency, since your account is in that currency, but this will be taken into account by the system as it converts all currencies to US. This is to make all advertisers the same no matter their currency to calculate ad ranking and CPC.
You can't change the currency so no.