Hello,

I am looking for information on how to update libraries. I have problems with Persistence of Vision ray-tracer that requires libpng12-0 update but I don't know to do this. I am asking this because I suppose learning how to do this would be of benefit in future.

Try using your package manager to start. If the latest version (or at least the minimum version you need) isn't available via your package manager, you can build the library from source.

What distro are you using? And what version of libpng12-0 do you have and which one do you need? In Debian Testing, which I'm running, the current version is 1.2.50-1. I see this same version is also being used in Debian Unstable (Sid).
jdk

I am using Ubuntu 14.04. My language pack is finnish. The problem is as follows:

I have downloaded file povray_3.6.1.1-12_amd64.deb from Internet. When I try to install it, Ubuntu gives me the following error:

Violates existing packet 'libpng12-0' which is contradictory with following: 'povray-3.5'. But /home/kkoistinen74/Lataukset/povray_3.6.1.1-12_amd64.deb gives it as follows: 'povray-3.5, povray-3.6'

I assume I should do something (upgrade?) to libpng12-0 but don't know how to do this or what to do. Naturally above error is translated from finnish.

But what version of libpng12-0 do you have installed now. And why do you need to download povray from the internet. You should be able to install it with your package manager. This is what weibullguy already suggested. The package povray exists in the Debian repos so it should be found in the Ubuntu repos as well.
Tietysti.
jdk

My version of libpng12-0 is libpng12-0 1.2.50-1ubuntu2. The reason why I have to download povray from Internet is that I am unable to install it through normal Ubuntu software installation. It is very likely that I am doing something wrong here. Should I try to install povray through apt-get in terminal? What should I type?

Edited later:

I managed to install Povray through information in Internet. Thank you all for help with this issue.

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jdk