Can I increase the height of a DPC

Hi. Why don't you install a French drain to perimeter to reduce the ground level. It would be ill advised to replace a fully functioning dpc with a new chemically injected one

Ideally you want to keep your DPC low as possible, remember the high you go the more chance you've still got of mositure traveling up and also ng the no forming barrier ie(dpc) if you've got a failing dpc you can sometimes drill along the same one depending what dpc if any you had before, i.e. Copper wire, all you've got to remember is you've got to allow the injection cream to foam a straight barrier and as close to the inside floor as possible, best way to get best results inject both side of the area that need the dpc if accessible. Hope this helps.