You can manage various parts of your account configuration through the account settings tab in the Admin.
Your Time Zone is set on creation of your account and is used for knowing when to send Slack and Email notifications.
You can find the setting in: Admin → Account → Time Zone
Start of Week
You can adjust the Start of Week Day to suit your region. This is useful when configuring KPIs and Budgets that match what you consider to be a week.
Changing the start of the week will change all KPIs and Budgets set on a Weekly tracking schedule to convert to the new setting.
You can find the setting in: Admin → Account → Start of Week