How to safely upgrade svn on ubuntu 16?

I am running svn on Ubuntu 16.04.6 LTS.
It reports the following:
$ svn --version
svn, version 1.9.3 (r1718519)
   compiled Aug 10 2017, 16:59:15 on x86_64-pc-linux-gnu

The Ubuntu machine acts as a backup for a Windows 16 based VisualSvn
server running at a separate location.
Backups are performed using nightly svnsync commands via the Internet.

The Ubuntu machine and svn were setup for this purpose about a year
ago and since then Ubuntu has been kept updated using apt upgrade and
apt dist-upgrade as adviced on the login screen when I regularly check
in via PuTTY.

But it seems like svn is not being touched by these operations....

So what is the advice on what to do in order to at least get to the
latest 1.9 stable release of svn on this machine?
It seems like that would be 1.9.10...

Since this is a production backup server I am reluctant to risk
breaking it, obviously.

-- 
Bo Berglund
Developer in Sweden