Can anyone help I'm a bit of a beginner I'm on Debian 10 KDE plasma 5.14.5 how do I update to 5 20?

You should read about how Debian gets updates, upgrades and dist-upgrades. It won't be possible to upgrade to newer versions but by adding different sources to get newer versions → but this gives the maintainer of this source root permissions on your device and could also break the system.

If you really need a newer version, use a distribution shipping it. Debians policy is to support its version for a long time, not upgrading it.

ok thanks probably leave it then but when i go into discover settings software sources the run as root-kde su box freezes/hangs how can i fix this

What do you start exactly? What are the error messages? What does the journal contain? Normally you should not start any graphical tool as root. If advanced permissions are required, there will be a popup asking for a valid password using PolicyKit.

Debian also has a great Wiki and manual.

in discover i click on settings then software sources in the top right box pops up asking for root password just stays there hangs ? there isn't any error messages

No Logmessages at all? There should be some warnings at least, including a binding loop at startup (which is nothing to care about) and the PolicyKit request is logged too. What logfiles did you search at? Do you get usable output starting plasma-discover in a Konsole instance?

The box just stays there nothing happens

https://manpages.debian.org/buster/systemd/journalctl.1.en.html