I want to flip over the values in my legend so that I have Low : 0 at the top, and High : 199998 at the bottom. I have manually edited the text in the table of contents, however this doesn't change the data values, they remain the same. I have gone to the symbology properties to try and edit the labels, but when I try to edit the in 'labelling' it reverts back to the original value when I go to change the next value.
I do not know how to do this in the Table of Contents, but you can use this little trick to make it display how you want it in the Legend on your layout.
Symbolise your raster how you want it shown with the high and low labels matching the colours you want them attached to (High at the top, Low at the bottom as is the default).
Duplicate your layer (Hold down Ctrl and with the mouse drag your layer up in the table of contents. This should create a new copy of your layer). Turn off that new layer in the TOC.
On your new layer copy, change the High/Low labels to how you want it displayed on your legend. Open the layer properties and select Invert to flip your colours so the labels and colours now match.
You should now have two rasters in your TOC, one used for display, and one to be used for the legend
Create your legend, selecting your new layer copy. Once your legend is created, double-click on it and de-select the option "Only show layers that are checked on in the Table of Contents" to make your layer copy display in the legend
Your new legend will show your raster ramp with Low at the top and High at the bottom.
I have read (although I can't find the link now) that it's a bit backward to have the Low value at the top and the High value at the bottom just due to the fact that Low should be down towards the bottom of the page and High should be up towards the top of the page. I can see the logic in this, but it would be nice to have the option to check on (like the "Invert" option for flipping the colour ramp) to allow us to flip the values on the ramp as well.