You may have come to several pages that tell you:
Before installing X, please first do sudo apt-get update && sudo apt-get upgrade. Sometimes they may say sudo apt-get update && sudo apt-get dist-upgrade. But what is the actual difference between the two? And what should you use?
TL;DR: Always use the dist-upgrade because it's more comprehensive and intelligent but it may break stuff.
Upgrade itself just installs all new versions of software that is already on your computer. It gets all the new packages and then installs them. There is no uninstall involved. Only works after update.
Dist-upgrade is like upgrade but it also tries to solve conflicts between versions of installed software. It tries to solve those intelligently and when in question, will upgrade more important packages even if less imporant ones need to be removed to achieve the upgrade. Additionally, its settings can be adapted via apt_preferences.