1 – Right click on the current material being used in the materials bar
2 – Click ‘Select Texture Tags/Objects’ (they should highlight on the objects being used)
3 – Right Click on the new texture you wish to replace with and choose ‘Apply’
4 – The new textures should be hierarchically above the old texture.
5 – Right click on the old material being used in the materials bar and re-select
6 – Click Delete, this will remove them all from the objects they are on…