To edit Vehicle Reminder Settings, click on your username at the top-right of the screen (1) and then click Settings (2):
On the left-hand side of the screen, use the scroll bar (1) to scroll to the bottom of the list. Once you have reached the bottom you will see Reminder Settings (2), click on Reminder Settings:
You can then modify settings by clicking on values in the Value column (1). The values will turn blue when you place the mouse over them:
In the above example, reminders will turn RED when due in 5 days or less and YELLOW when due in 14 days or less. The red colour will always override the yellow colour.
The same principal above can be applied to HOURS and KMS
After changing the setting, press Enter on the keyboard to save, or change your selection.