IMPORTANT FIRST STEP

RESET ALL TRACKS IN TRACKMAN THEN CLOSE IT

1 - Copy and paste the track file ( tra or trk ) into a copy the resmkres2010 folder that you downloaded from this page ( updated files to decompile and compile a vr car or track image ).

2 - Right click on the "unpack.bat" file,choose edit,type the name of the track where is says trackname.tra ( example.tra OR example.trk ).The file extension of the track is important.Now click the x to exit that bat file and click YES when ask to save changes.

3 - Now to open the track file just double click the "unpack.bat" file.

4 - A bunch of files should have been extracted into the folder you are working in.Now double click the "ResClean.bat" file.

5 - To convert all the ".tex" to ".tga" files readable by a paint program files,double click the "tex2tga.bat" file.

6 - Now you are ready to "retexture the track" , which actually means you will be changing all or some of the textures ( the colors of the stuff you see when driving on the track ).To quickly view tga files I use a Free program called Irfanview.Get Irfanview here.

7 - Import the tga file of your choice into your fav paint program ( gimp is free ).Link to Gimp here.

8 - Look at the texture and see if all you need to do is darken it or blur it.If you can modify it like that you can save a lot of hassle.If you want to change it completely,import the tga,jpg,bmp or any image file into the paint program with the original you have in there.

9 - Here is an example of what I mean if you just want to change 1 texture:
Say your grass.tga file was lime green and you wanted to use an actual grass image from the internet.Import that pic into your paint program.Copy and paste it into the grass.tga.Now just save that image as you see it.Say yes if asked about a merged image or whatever.It retains the same name so it is ready to be converted into a grass.tex file so the track can be put back together with that texture.
IMPORTANT NOTE
Make sure your paint program is set to export a tga file as a 32 bit Uncompressed option.
To do that it is probably easiest to export a test.jpg file as a test.tga file in the "save as " choice and check the options box.

10 - Once you finished doing all the textures you want,go to the tga2tex folder and follow the instructions in the readme in that folder.Textures that have an "alpha" channel ( see thru ) use a diff bat ( batch ) file to convert tga to tex files.For example 99% of trees have an alpha channel but 100% of road and grass textures do not.

11 - Once you have done that copy and paste the files from the converted folders into your main track extraction folder overwriting the old ones.

12 - Right click the mkres.bat file,choose edit,type the exact name of the original track ( lower and upper case exact ) then close and save.Next step is the easy-peasy final one.

13 - Now you can double click the mkres.bat file to put the track back together with your textures ( it will overwrite the original one in that folder without asking to confirm ).Copy and paste that track into your data folder overwriting the original one.
You Are Done!