UI text small

[Großer langer Schwanz Joe]

How do I make the UI text bigger running on 4k on a 50 inch

[Sethreal]

RIFT has a very scaleable UI, it's one of it's strengths.
Settings > Interface > Display > Global UI Scale (Percent)

You can also scale individual parts of the UI, just look through "Settings > Interface" tabs and look for things that mention scale. For example:
Settings > Interface > Player Name Scale (Percent)

Edit: When you've made the UI to your satisfaction, be sure to use "/exportui" to save it and then "/importui" to load it on other characters.