Consider a uniform cylinder immersed in a liquid!.
Force on the upper face of the cylinder = hρgA
Force on the lower face of the cylinder = [h + L]ρgA
Difference in force = LρgA
But LA is the volume of liquid displaced by the cylinder, and LrgA is the weight of the liquid displaced by the cylinder.
Therefore there is a net upward force on the cylinder equal to the weight of the fluid displaced by it.
The same result will be obtained for a body of any shape, regular or not by taking into account the vertical and horirontal components of the forces on the object.
If a sphere of radius r made of material of density σ is fully immersed in a liquid of density ρ the apparent weight of the sphere is given by:
Apparent weight = actual weight - upthrust = 4/3 πr3g(ρ - s)