If you are using third party items you will need to wait for each one to be updated for 4.5 or confirmed the current version is working with 4.5. Since 4.5 hasn't been released at this point, nobody is working on updates just yet, once developers get their hands on beta versions they can start developing and testing for any needed changes.
If you are not using any third party items, then once the final version is released, you can upgrade without issue!
If you have a very large site or items of concern, and are self hosted, you can always do a test install to test your upgrade process and third party items before doing your live community if needed.
The final golden rule, always do a backup of the database and file system before upgrades, things can sometimes go wrong, so it's always nice to have a quick restore as an option rather than freaking out if your community is troubled with an upgrade issue.