M6, M42, M40 to J4, A404, A404M to join the M4. You'll see the stadium from the Motorway.
M6, M42, M40 J9, join the A34 and join the M4 at J13.
Parking at the stadium is quite easy and convenient on your arrival. but it is a bit of a mare to get off afterwards. Bristol Mick advised me last week to try the nearby Greyhound Stadium, so I might well do that.