  It is found that the exact beta-function $\beta(g)$ of the continuous 2D
$g\Phi^{4}$ model possesses two types of dual symmetries, these being the
Kramers-Wannier (KW) duality symmetry and the weak-strong-coupling symmetry
$f(g)$, or S-duality. All these transformations are explicitly constructed. The
$S$-duality transformation $f(g)$ is shown to connect domains of weak and
strong couplings, i.e. above and below $g^{*}$ with $g^{*}$ being a fixed
point. Basically it means that there is a tempting possibility to compute
multiloop Feynman diagrams for the $\beta$-function using high-temperature
lattice expansions. The regular scheme developed is found to be strongly
unstable. Approximate values of the renormalized coupling constant $g^{*}$
found from duality symmetry equations are in good agreement with available
numerical results.
