I didn't find a definition for the upper median (or lower), but my guess would be the following:
If you have $2n$ samples for $n \in \mathbb{N}$ and $x_i$ is the i-th lowest value, the lower median is element $x_{n}$, the upper median is $x_{n+1}$ and the "normal" median is $\frac{x_{n}+x_{n+1}}{2}$
Is this correct?