Press ~ and the in-game console will appear.
If it doesn't appear go to Game Options and make sure the console is enabled in the game settings.

1) Change FOV with console command
Type (cg_fov 90) when the mission starts.(once if you change FOV in the mission you no need to change it everytime you restart the game.)

2) To change to fullscreen go to this
Example path ("D:\Steam\steamapps\common\Call of Duty
2\main\players\Playername\config.cfg") where you installed the game.

3) Open config.cfg file and change seta r_fullscreen "0" to value 1 to enable fullscreen mode.

To Fix Multiplayer Blank Black Screen

1) Go to steam main folder C:\Program Files (x86)\Steam(Example path where you installed
steam).

2) Find a file called Steam.dll and Steam2.dll, copy it and
Go to C:\Program Files (x86)\Steam\SteamApps\common\Call of Duty 2 (Example path where
you installed game) and paste there.

3) In the same example path folder Right click on COD2MP_s and change compatibility to
Windows XP Service pace 3 and click on apply.
Follow step 2 & 3 to solve the multiplayer issue.

4) Remove 91 FPS cap in multiplayer.

To fix this Look for seta com_maxfps 85 in your config_mp.cfg file and set 85 to 0.
config.mp fix is located in the Example Path ("D:\Steam\steamapps\common\Call of Duty
2\main\players\Playername\config.cfg") where you installed the game.

5) If Game crashes when changing any graphics setting

In the Graphics options menu, set the "Rendering Method Preference" to DirectX 9, apply it,
and then you can change screen resolution.

Important Notes:

1) While playing multiplayer,if you download new maps or mods it might effect the single player by
only showing the black blank screen.
To fix this cut/paste all the mods,maps,text files related to multiplayer and save it it other folder
outside the game folder.Only copy them back to game folder when you play multiplayer or else
single player might not work.
2) If you are not aware of it or confused then make a backup of config.cfg file and then right click on
game in steam ,select local files,verify integrity of game files.
This should set the game to default and copy back the config.cfg to the example path folder
("D:\Steam\steamapps\common\Call of Duty 2\main\players\Playername\config.cfg").
(This results in loss of multiplayer files but single player works as usual).