It isn't too hard to find Blenheim (Blindheim) on a map: it is just north of the Danube, about 22 miles north-north-west from Augsburg. However once you reach the village your troubles begin!
Head for the church in the middle of the village, outside of which there is a display board with some information about the battle and a sketch map - with the emphasis on "sketch"! Head back to the north and take the second on the left, which should be Oberfeldweg. Follow that along till it rises up to a bridge across both road and railway line and you will find the metal tower just over the bridge.
To find the second memorial is more difficult - I had to ask a chance passerby, who kindly pointed it out to me. Recross the bridge, at the bottom of which you can turn left down a dirt track which looks like a farm track - it probably is. Follow it to the bitumen road and turn left. A hundred yards or so down this road you will see on your left a flight of steps. You can probably park in a field entrance on the right, cross the road (carefully) and climb the steps.