The "Change" column of the Metrics Summary chart shows two numbers: an absolute value and a percentage. The absolute value is the difference between the value in Column 1 and the value in Column 2. In the screenshot shown below, the Source EUI is 248.2 in Column 1 and 259.2 in Column 2. So, the "Change" is 259.2 - 248.2 = an increase of 11.00 kBtu/ft².
The bottom number is the relative change, which shows how big the absolute change is in proportion to the initial value. 11.00 is 4.40% of the initial value of 248.2, so this change was a 4.4% increase in EUI. Relative change is also known as the delta and is calculated by dividing the absolute change by the initial value and then multiplying it by 100 and expressing the result as a percentage.
What does the text color mean? Change in a "good" direction in terms of improved efficiency or emissions is shown as green text in this column, and change in a "bad" direction is red text. Neutral changes appear in black.