I assume that you already have taken both partial derivatives.
When we want to find a suitable integrating factor, sometimes it's not so easy, so we may introduce the following cases.
CASE I. Integrating factor dependent of Suppose that
it's a function that depends only of
which we'll denote it by
Then, an integrating factor for the given equation is
CASE II. Integrating factor dependent of
If we have that
it's only a function of
denoted by
then
is an integrating factor for the differential equation on the form
CASE III. Integrating factors of the form
If they exist
and
such that
then
is an integrating factor for the differential equation mentioned previously.
CASE IV. If they exist functions
y
which satisfy
then an integrating factor for the differential equation is
Note that the case IV includes to the cases I, II y III if we take
and
respectively.