  We present updated empirical radio surface-brightness-to-diameter
($\Sigma-D$) relation for supernova remnants (SNRs) in our Galaxy. Our original
calibration sample of Galactic SNRs with independently determined distances
(Pavlovic et al. 2013, hereafter Paper I) is reconsidered and updated with data
which became available in the past two years. The orthogonal fitting procedure
and probability-density-function-based (PDF) method are applied to the
calibration sample in the $\log \Sigma - \log D$ plane. Orthogonal regression
keeps $\Sigma-D$ and $D-\Sigma$ relations invariant. Our previous Monte Carlo
simulations verified that the slopes of the empirical $\Sigma-D$ relation
should be determined by using orthogonal regression. Updated calibration sample
contains 65 shell SNRs. 6 new Galactic SNRs are added to the sample from Paper
I, one is omitted and distances are changed for 10 SNRs. The slope derived here
is slightly steeper ($\beta \approx 5.2$) than $\Sigma-D$ slope in Paper I
($\beta \approx 4.8$). The PDF method relies on data points density maps which
can provide more reliable calibrations that preserve more information contained
in the calibration sample. We estimate distances to five new faint Galactic
SNRs discovered for the first time by Canadian Galactic Plane Survey and
obtained distances of 2.3, 4.0, 1.3, 2.9 and 4.7 kiloparsecs for G108.5+11.0,
G128.5+2.6, G149.5+3.2, G150.8+3.8 and G160.1$-$1.1, respectively. The updated
empirical relation is used to estimate distances of 160 shell Galactic SNRs and
new results change their distance scales up to 15 per cent, compared to results
from Paper I. The PDF calculation can provide even few times higher or lower
values in comparison with orthogonal fit, as it uses totally different
approach. However, in average, this difference is 32, 24 and 18 per cent for
mode, median and mean distances.
