I signed up for adwords account and chose british pounds. Can I switch to $$$ or I have to open another account? If I cant switch, can I just close old account?
as I know is not possible to switch to another currency - contact support to be sure. you need to open another account - be sure to delete all your old campaigns to avoid double campaigns running (this is against TOS) notice that if you are from uk you will not be able to use prepayment option in a USD account.
Is against TOS if you run both in parallel at the same time for the same keywords and for similar business (same landing page). Just create a MCC account and put both accounts under the same MCC account and be sure to never run both at the same time. Also with the MCC parent account you can switch between both accounts with just a click without a need to login / logout every time Your first step is to get a MCC account: https://adwords.google.com/support/bin/answer.py?answer=22531&ctx=sibling