This is really easy! Just pull the guide/braid assembly straight down, very gentle leverage with a blunt knife blade may help..
Replace the braids, it is best to pre bend them to the dimensions of the old ones. Put the new braids in place, making sure that the parts that sweep the track rails are facing the right way!!! The 1st time you do this it is best to do one braid at a time, and certainly one car at a time.. (Once you have done it once this instruction may seem over cautious)
Finally make sure braids are tight and well seated on guide/braid assembly, and press the whole assembly straight up back into place.
Economy tip.... When the braids are worn/dirty from use they can be turned over and/or turned end to end to present diferent surfaces to the track, this is best done before the braids get too worn and untidy, but however bad they seem, an end to end change will be easily possible.
Please see my other guides, and, if you found this helpful please "like"