Determine if the following change is an oxidation, a reduction, or neither
As pointed out in the comments and the other answer, it is neither an oxidation, nor a reduction.

Q: So, what is it?

A: It is a condensation: two molecules of an ortho acid combine under loss of one molecule of water to yield a diacid (pyro acid).

This is frequently found in oxoacids, see


$\ce{H3PO4}$ (phosphoric acid) and $\ce{H4P2O7}$ (diphosphoric acid)
$\ce{H3AsO4}$ (arsenic acid) and $\ce{H4AsO7}$ (diarsenic acid)
$\ce{H2SO4}$ (sulfuric acid) and $\ce{H2S2O7}$ (disulfuric acid)