Step 1 : Open the file with the correct blender version (3.6 or above).

Step 2 :  Select the tree and go to the modifier tab if not yet selected and you will have all the parameters needed to customize your tree.

All parts of the tree can be disabled except the trunk with the booleans named "Enable/Disable" to get more control over each part of your tree.

If you need to switch from procedural material to a custom texture you can go to the "Shading" tab and select the material you wish to modify.

For the Bark material you only need to plug the Color from the Image Texture in the base color of the Principled BSDF and then add your custom image.

For the Leaves material you only need to plug the Alpha output of the Image Texture node into the Alpha of the Principled BSDF and then add your custom image.

For Game Engines you will need to assign the correct UV map. There is one for the leaves and one for the bark. In Unreal Engine it corresponds to the TextureCoordinate node which you will have to set to 0 or 1 depending on the texture.