The start point of a G2/G3 arc is the current position.
The center of the arc are the I and J coordinates, relative to the start point.
I=X
J=Y
Since your start point is 0,0, and your IJ coordinates are 2,2, the center is at 2,2 (0+2)
The end point is specified in the G2/G3 move, in this case, 4,4.
So, you're cutting an arc that starts at 0,0, and ends at 4,4, with the center at 2,2.
Say you wanted to move the circle 2 units to the right, and 1 unit up. You just need to change the start and end points.
G0 X2.0 Y1.0 (arc starts at 2,1)
G0 Z1.0
G1 F300.0 Z-0.4
G3 F800.0 X6.0 Y5.0 I2.0 J2.0 (arc ends at 6,5)
Note that the center is relative to the start point, so the center is now at 4,3, even though the I and J coordinates are still 2.
X center = 2+2 = 4
Y center = 1+2 = 3
So you now have an arc that starts at 2,1, ends at 4,4, with the center at 4,3.
Forgot to mention that G2 arcs are CW, and G3 are CCW.