When you die, your DP level is typically reset to its level when you triggered the last checkpoint. However, you can avoid losing points by using the points to purchase an upgrade. Use this to your advantage. Find a place where you can easily obtain large quantities of DP. Do so, then purchase a desired upgrade and die on purpose. You'll resume from the checkpoint with the upgrade still in place and then you can earn more points and purchase another upgrade. Repeat it as often as you like, until you have the upgrades that suit you.