It's not that difficult, but just like all other things to do with your pc, if you are not sure, it's better to leave something alone.
However, if you want to try it anyway, here's what you do:
Go to your Shipsim 08 directory. (The folder where it is installed on your hard drive)
Example: C:\Program Files\Vstep\ShipSim2008
Open the folder called "Actors" and in that folder, open the one called "Objects".
Then you'll see all the folders for the ships and such. Find the one called "Titanic" and open that.
In there, you will find a file called "horn.wav".
This is the soundfile that is played when you sound the horn ingame.
Rename this file, let's say to "original_horn.wav"
Then grab the file that Thirdmate has linked to, and rename that one to "horn.wav" and put that into the Titanic folder.
Now, the new file will be the horn.
If you prefer the original one, after trying it out, just throw the new one away, or take it out again, and rename the original one to "horn.wav". again.
And like this, you can replace any of the horns in any of those folders for the ships.
But make sure you rename the original one to keep it as a backup. You can also put it elsewhere for safekeeping instead of renaming it, but I prefer renaming, then it's always clear what it is..
(the original horn, in this case, as that's what it's name is..
)
Easy job, if you follow these steps.
Regards,
Fred