Default [Q] SGH-M919V software stuck on andriod 4.3

Hi,
I bought an the Galaxy s4 model SGH-M919V of ebay so I can use it here in Canada for the wind mobile network. The phone works well with the network and everything. The SGH-M919V model I have is actually a NEXTEL phone.

When I do a software update for my phone it tells me "the latest updates have already been installed" but I am rocking andriod version 4.3 while kitkat is out as well as other software versions.

My question is, am I supposed to wait for WIND to release their new updated version for the s4 since I am using their network or wait for NEXTEL since it is their phone?

Please mind I am new to this whole andriod stuff and this is my first andriod phone.
Thank you