The correct tool to get the crank bolt out is an 8mm hex wrench (allen key).
Now you need a bottom bracket spline tool. This will engage the splines of the cup holding the bottom bracket (shaft and bearings) in the frame. then you need to remove the other crank arm (this time with an 8mm allen key to remove the bolt and crank puller to pull the arm off the spindle. An angle grinder is not the correct tool) and remove the cup from the other side.
NB the left cup that you already have access to is RH threads, so normal counter-clockwise to remove, and the right side (drive side) has reverse threads, so is clockwise to remove.