Do I update?

I have 13.5 gigabytes on my (C:). I have a 10 gigabyte update that isn't mandatory, but includes W11 features and most importantly, security features.

What update do you have that is 10GB in size for Windows 11?

Either way, more and more updates are going to be coming out. You might need to spend some time cleaning up your hard drive to make more space available, or you may need to start saving up for a new larger drive.

Should go onto setting/storage and cleanup thus updates cleaning

You're going to have to have more drive space or you're going to run into problems. You can try running disk cleanup and then delete or move any files and folders you don't need on drive C:. I hope you don't have one of those inexspensive laptops that come with a very small drive C: that is soldered in and can't be upgraded.

Unless one wants performance to suffer, it is smart to retain enough free space on your system partition to handle all that is demanded by Windows for use as swap space, cache space, updates, windows.old folders, etc. Some say the amount of necessary free space should always be more than 30gb, but in reality it could be much more depending on how efficient the user is at file management utilizing the space he has available. My personal rule probably takes it to the extreme as I always keep as much free space on my OS drive as I have used space. Then I don't have to worry about it. In this day and time, storage comes in many forms and is too cheap, so there's no excuse to let a drive get full. Just my opinion.