To change it, go to the Settings page -> Date & Time tab. When comparing the current period to a prior period, users typically prefer to align the periods such that there are equal numbers of each day of the week in each period (the default setting of "Same day of week"). For example, if the current period is January 1, 2020 (Wednesday) to January 31, 2020 (Friday), the prior year would be January 2, 2019 (Wednesday) to February 1, 2019 (Friday). If you change the setting to "Same date" then the prior year period becomes January 1, 2019 (Tuesday) to January 31, 2019 (Thursday). This would be the preferred setting if you wanted to compare holidays such as Christmas in one year versus the prior year.