Cannot upgrade unsupported version of Skype for Linux (v5)

Solution 1:

Skype.com says:

Important notice: All Skype for Linux clients version 4.3 and older will be retired on July 1, 2017. To keep chatting, please install the latest version of Skype for Linux.

It's enough to add the official skypeforlinux source and upgrade your current installation with these commands:

sudo add-apt-repository "deb https://repo.skype.com/deb stable main"
sudo apt update && sudo apt upgrade

Alternatively, remove it with sudo apt remove skypeforlinux and install the current version from here. This will also add the source for updates to your sources, thus keeping the program automatically updated.

On upgrading to 17.10 the skype repository might get disabled so that you need to reenable it either in the Software Center or by editing /etc/apt/sources.list (do that only if you know what you do).

Solution 2:

In 32 bit linux, make skype a "higher" version:

sudo sed -i 's/4\.3\.0\.37/8\.3\.0\.37/' /usr/bin/skype

It replaces the version number in the binary for a higher one to work around the forced incompatibility. Make sure that you have the same version 4.3.0.37 by calling skype --version or update the command accordingly. Thanks to YuriyKuzin.