I've got monitor trouble

[cub3s]

Hi I'm looking for some help. I have a Benq GL2250 Monitor which I am using to display my computer through the DVI port. I have bought a hdmi cable to mini display port to connect my macbook so I can switch from my computer to my mac easily all on one screen but I can't seem to get it to switch from DVI to HDMI. This might be really stupid but is this possible to do having both plugged in at the same time?

 

[affinitydesigns]

You can try this: https://www.youtube.com/watch?v=tM-L6cAFmRk
That might work for you.