Hey we are running a caimpaign currently and all characters i noticed are using 2014 rules where a new caimpaign i started are using 24.  Different spells features feats etc.  How do I update old caimpaign to 24 rules

Everybody would need to rebuild their characters with the 24 classes. This is a bit annoying, but not hard.

1. Each player should make a copy of their old character, for reference and safety's sake (If they can't due to lack of slots, you, as the GM, presumably can.)
2. They should delete their current class (except artificer) (In the original character. The copy won't be in the campaign by default, so lacks any access to content sharing.)
3. They should pick the new core rules class, level it up, then make all the decisions required (this is also a good time to let players tinker if you want)
4. When picking things like spells and items, it's easier if they turn off "2014 core" in the builder (but a few subclasses are only available with this option on. They can turn it off after picking their subclass)
5. They can also replace their species and background, but it may be easier to have them leave those.
6. They may need to fix their stat allocation
7. If anybody takes a new background, you should let the people who leave it on old backgrounds take an origin feat of their choice ("manage feats" under the features and traits tab of the character sheet).
8. Have them replace old magic items with the updated versions
9. There may be a few things like skills and languages where they've lost things they had due to the numbers changing. You can let them add those back.

If anybody doesn't want to update, nothing will go wrong if they don't, though I strongly suggest having them update all their spells and items, so you don't have to keep track of two slightly different versions of counterspell or whatever.