Can I change the partition size after installing the bootcamp or I need to reinstall it all?

You’ll need to delete the partition and repartition again.

the reason is because they use different file systems: Windows uses NTFS (Windows NT File System) and macOS uses APFS or MacOS Extended (Journaled).

just like you can’t copy files from your Mac to your windows partitions and your Windows can’t read the Mac partitions, these file systems are not recognised by them.

Make sure to have a good backup of both macOS and Windows before doing anything since it could make the computer stop booting and potentially lose access to the data on both partitions.

Also only use BootCamp Assistant to remove and add the Windows partition.