[Q] LG Models differences topic

Hi Guys!

Please can anyone explain me what is the difference between a LG E-615, E-615f and LG Optimus L5?
My question is about this:

I wanted a DUAL sim phone with 3G behaviour in the 900 and 1900 Mhz bands. My seller told me that the LG-E-615 was the one. If some one check this model at gsmarena.com it look like it is ok. But it´s not. This model only has 3G features at 900 and 2100 Mhz bands.

Is this a ROM feature?
Can I upgrade to a new one in order to gain 3G behaviour at the 1900 Mhz band? or there is a hardware restriction?

Thanks a lot for your tips and responses,

Regards,

Jean L

Phone details:

Model: LG-E615
Android version: 4.0.4
kernel: 3.0.8-perf
Software version: V10g-APR-23-2013
Compilation: IMM76D