Is it possible to change the account currency?

It is not possible to change the account currency, however a new account in a different currency can be created and the money from your existing account can be transfered to this new account.

What is the difference between a regular account and a global account?

The default account type is regular or “hedging account”. On a Global type of account, you cannot open opposite positions in the same instrument. Each instrument has Net position without a possibility to place Stop Loss and Take Profit orders. The account can be switched from Regular to Global type if all positions are closed.