Is ther a way that a novice can replace these with real airlines,if so how?

Yes.  The way I did it will change Orbit and Landmark, etc. to real airlines.  Back up before trying this.

I will use the default 747s as an example.  AI/ATC recognizes the first 4 airlines so anything after that won't be heard on ATC.  Of course you could put 50 airlines if you wanted to and ATC would recognize your aircraft even if you were flying the 50th repaint but AI will only use the first 4.

First, obviously, you are going to have to download and install the repaints.  I recommend getting "repaint of default aircraft" because those are the only ones I have worked with.

After you have added 4 new 747 repaints (let's say Lufthansa, Swissair, American and Air Force One, because those are the ones I have) you need to reconfigure your aircraft.cfg so these 4 are at the top of the list and appropriately numbered (fltsim.0, fltsim.1, etc.).

The real important part is the "title=" entry in aircraft.cfg.  The first AI aircraft must read "title=Boeing 747-400", the second one must read "title=Boeing 747-400 Paint1", etc.  This is where ATC is going to look for the airline.

Then you will need to modify your "atc_airline=" to match the repaint.   After doing all of that here is what the first part of my aircraft.cfg looks like:
[fltsim.0]
title=Boeing 747-400
sim=Boeing747-400
model=
panel=
sound=
texture=
kb_checklists=Boeing747-400_check
kb_reference=Boeing747-400_ref
atc_id=N700MS
atc_airline=Lufthansa
atc_flight_number=009
atc_heavy=1
ui_manufacturer=Boeing
ui_type=747-400
ui_variation=Lufthansa
description= ... (edited out to save space)
visual_damage=1

[fltsim.1]
title=Boeing 747-400 Paint1
sim=Boeing747-400
model=
panel=
sound=
texture=1
kb_checklists=Boeing747-400_check
kb_reference=Boeing747-400_ref
atc_id=N700MS
atc_airline=Swissair
atc_flight_number=1123
atc_heavy=1
ui_manufacturer=Boeing
ui_type=747-400
ui_variation=Swissair
description= ...
visual_damage=1

[fltsim.2]
title=Boeing 747-400 Paint2
sim=Boeing747-400
model=
panel=
sound=
texture=2
kb_checklists=Boeing747-400_check
kb_reference=Boeing747-400_ref
atc_id=N700MS
atc_airline=AMERICAN
atc_flight_number=009
atc_heavy=1
ui_manufacturer=Boeing
ui_type=747-400
ui_variation=American Airlines
description= ...
visual_damage=1

[fltsim.3]
title=Boeing 747-400 Air Force One
sim=Boeing747-400
model=
panel=
sound=
texture=3
kb_checklists=Boeing747-400_check
kb_reference=Boeing747-400_ref
atc_id=AA001
atc_airline=Air Force
atc_flight_number=1
atc_heavy=0
ui_manufacturer=Boeing
ui_type=747-400
ui_variation=Air Force One
description=...
visual_damage=1

[fltsim.4]
title=Boeing 747-400 British Airways
sim=Boeing747-400
model=
panel=
sound=
texture=ba
kb_checklists=Boeing747-400_check
kb_reference=Boeing747-400_ref
atc_id=GR651
atc_airline=SPEEDBIRD
atc_flight_number=009
atc_heavy=1
ui_manufacturer=Boeing
ui_type=747-400
ui_variation=British Airways
description=...
visual_damage=1

ATC/AI will recognize paints 0-3.  I can fly the BA and ATC will call me BA but I will never see a BA AI aircraft.

Simple, huh?