Yes, the other way around would be multiplication by PI.
Lumens are the same as Watts, basically, you just have to multiply by some conversion factor, which says how much energy is actually visible and how visible it is (e.g. we are more sensitive to green light). There's a special function for that and it depends on spectrum of the light, but Corona uses a standard factor of 683 (see here:
https://en.wikipedia.org/wiki/Luminosity_function)
The rest is obvious, based on the quantities (steradians and meters squared), so the equations would be:
[W] = [Lumens] / 683
[W/sr] = [W] / PI
[W/(sr*m^2)] = [W/sr] / S
Where S is the surface area of the light, which of course will depend on the geometry of the light.
Lumens describe the light of the whole light source, Candelas describe light only in one direction, which makes sense only on average or if you know which direction you are talking about. Without going much into the detail, in our case, you can just use PI again:
[Lumens] = [Candelas] * PI
Edit: Lux is similar to Candela in that it describes all directions, but only in one point on the light source, so you don't use PI as the factor, but the surface area S:
[Lumens] = [Lux] * S