If the account is currently running on V1 and in order to switch to V2,you need to go to Settings-> General and there you will be able to see the V2 switch, which should be turned to On and then click Save Settings:




If the account is currently running on V2 and for some reason needs to be switched to V1, the corresponding drop down is located again in the General section:


*Sometimes you might need to log out and log in again after switching from V2 to V1 in order the UI to be refreshed.