Probably the default method for access LPAR console , is to use HMC GUI to access windows Console.
But there is a better way. Just enable ssh on the hmc (open by default)
ssh into the HMC using any tool like putty ssh.
once connected to the hmc,
#vtmenu
this will list the available managed systems
select the managed system using it’s number
to exit the LPAR console use tilde followed by dot. ~.
hope this will help