What game version are you running? Ensure you download the same version of Simple Trainer (trainerv.asi) as your game version.

You can see the upload history on the Simple Trainer mod page.

@ReNNie It is still technically a tutorial, some people prefer verbal instructions over written tutorials but if it is against the rules then so be it I will not post any more tutorials to contribute towards this forum board.

In order to play an older game version (Non-Cracked GTA V) you will need to replace the following files:

GTAV.exe
PlayGTAV.exe
update.rpf
common.rpf
gameconfig.xml
ScriptHookV

A quick search of older game version you wish to use can be found on Google or YouTube, for example:

"GTA V downgrade to 2245"

You will then need to "copy update.rpf / common.rpf to mods folder" because you cannot have a version mismatch between the game update.rpf / common.rpf and mods .rpf files.

To prevent the game from auto-updating and reverting all of the work you have just carried out above, you will need to install NoGTAVLauncher.

Unless the author of the modifications you have decided to install created a .OIV uninstaller then no, unfortunately you will need to uninstall manually.

You can find which files a .OIV installs by changing the .OIV file extension to .ZIP, open it with 7zip / WinRAR and open the assembly.xml file with a text editor such as Notepad / Notepad++.

You should now see all the paths the files are being placed into via the .OIV installer, now open OpenIV go inside the mods folder and delete the respective files accordingly.

Of course this can be a very time-consuming job if the installer contains many lines and therefore it may be easier just to wipe the mods folder and start again.

Use the heapadjuster.asi by dilapidated that is configurable, go into the .ini file and change the default value of 750 to 2000. Doing this will allocate more RAM to the game.

This is an in-depth video showing you how to merge NVE, QuantV and LA REVO manually.

If you have any questions, please do not hesitate to ask.