First open the program, and copy the samp.dll that you want to modify on the Desktop. Once this is done, press the button with the 3 dots inside the program, and select the location of the samp.dll, previously moved to the Desktop.
If the file will be recognized as compatible, you can start the modification by clicking on one of the
"Choose" buttons, corresponding to what you want to modify, or you can press the
"R" and
"RO" buttons to reset the previous colors.
Once you have finished changing the colors, click on the "Save" button to implement the changes on the samp.dll, or "Cancel" to stop the change and not make any changes to the samp.dll.
Once that is done move the samp.dll which is on the Desktop, inside the main GTA San Andreas folder, and you're done! In case you want to restore the old samp.dll, at the time of the modification a file with .bak extension will be created, in the same folder where there was the samp.dll that you modified, in this case on the Desktop. To reuse it, simply remove the .bak extension, and if present, also the number that identifies it, for example: .bak1, .bak2, etc.