Partitioning SD card to use as int memory..welp..!!

I am having the same universal internal memory full problem for my phone Canvas Magnus.
So, I rooted my phone and i am aiming to create a partition on my SD card and use it as an internal memory. I am following a guide which says to do so by using APart+BUsybox (for partitioning without PC) and then link the partition by using Link2SD.
the procedure for creating the partition says that in APArt I will be prompted for partition making.
but this is where I am stuck -
The guide clearly takes into consideration the extSD for partitioning as in APArt detects extSD by default for partitioning. But in my phone there is an IntenalSD, which is getting detetced by APArt for partition.
I cant even go further with intSD because, APart can only partition when the SD card is unmounted.. and there is no such option as unmount internalSD card, only the opposite - unmount extSD.
I dont understand how to get APArt to select extSD as THE SDcard to be partitioned.

Can anyone please help..??

 

thanks .. i ll go for partitioning using PC ..!!