  We have studied the temperature dependence of the upper critical fields,
$\mu_{0}H_{c2}$, of K$_{x}$Fe$_{2-y}$Se$_{2-z}$S$_{z}$ single crystals up to 60
T. The $\mu _{0}H_{c2}$ for $H\parallel ab$ and $H\parallel c$ decrease with
increasing sulfur content. The detailed analysis using
Werthamer-Helfand-Hohenberg (WHH) theory including the Pauli spin-paramagnetic
effect shows that $\mu _{0}H_{c2}$ for $H\parallel ab$ is dominated by the
spin-paramagnetic effect, which diminishes with higher S content, whereas $\mu
_{0}H_{c2}$ for $H\parallel c$ shows a linear temperature dependence with an
upturn at high fields. The latter observation can be ascribed to multiband
effects that become weaker for higher S content. This results in an enhanced
anisotropy of $\mu _{0}H_{c2}$ for high S content due to the different trends
of the spin-paramagnetic and multiband effect for $H\parallel ab$ and
$H\parallel c$, respectively.
