Your balance is displayed in your account detail view as well as on the dashboard. To access the dashboard, simply click on "Dashboard" on the top left.
On the left hand side, you will see your current balance, right above the past 6 months statistics.
The account detail view is accessed by clicking on your name to the top right and selecting "Your Account" there. Here, you can also transfer credit to or from your account.
For a further breakdown of the current month's balance, you can go to your "Account Summary" page by again clicking your name at the top right, followed by "Your Account" and then "Account Summary", or by clicking here: https://app.gotphoto.co.uk/config_balance/account_balance