I have enough space then also not able to update the ios

If your device won't update, make sure you are following all the conditions for the method you are trying to use:

Update your iPhone or iPad - Apple Support - wirelessly

Update iOS on iPhone - Apple Support - with a computer

If your Apple mobile device won't update, read this support article for a list of things to try --> If your iPhone or iPad won't update - Apple Support

Another, less common reason for not being able to update is if you were using a beta version of software. Refer to How to uninstall iOS or iPadOS beta software - Apple Support