If updating from an existing 0.3z server: you can update simply by replacing the 'samp03svr' file on linux, or 'samp-server.exe' file on Windows, found in the 0.3z server download package.

Important: If your script uses the OnUnoccupiedVehicleUpdate callback, you will need to recompile your scripts with the latest pawn includes to use this server update.

SA-MP 0.3z R4 server

We received some reports that players might be able to use the vehicle trailer syncing in order to move vehicles around on the server without being in control of them.

- Additional sanity checks have been added to the trailer validation on the server.
- A new callback is added to identify players updating their vehicle's trailers:
 

public OnTrailerUpdate(playerid, vehicleid); 
// playerid is the player who sent a trailer update. vehicleid is the trailer being updated.
// Returning 0 to this function will stop the trailer update being sent to other players on the server. The trailer's position will still be updated internally on the server.

- The OnUnoccupiedVehicleUpdate is updated to include the new velocity of the vehicle updated.

public OnUnoccupiedVehicleUpdate(vehicleid, playerid, passenger_seat, Float:new_x, Float:new_y, Float:new_z, Float:vel_x, Float:vel_y, Float:vel_z);
// If your script uses this callback, you will need to update this definition and recompile your scripts to use the 0.3z-R4 server.

- Removes script HTTP debug messages left in the 0.3z-R3 server.

SA-MP 0.3z R4 Linux Server: http://files.sa-mp.com/samp03zsvr_R4.tar.gz
SA-MP 0.3z R4 Windows Server: http://files.sa-mp.com/samp03z_svr_R4_win32.zip
SA-MP 0.3z R4 Linux Server (1000 max player): http://files.sa-mp.com/samp03zsvr_R4-1000p.tar.gz