Hidden C: Drive Partition contents. How to safely reduce size

I did a Win 11 installation on unsupported hardware following advice elsewhere on this forum on a Dell Inspiron Laptop. Under normal circumstances I would do a clean install but there was software on the laptop I needed to retain as I don't have the serial numbers.

I now have a running Win 11 install but the disk partition structure is "non standard". I believe this is because Dell create an OEM recovery partition that their proprietary recovery software uses. (Note this was a windows 7 laptop that was automatically upgraded to Win 10 during the free rollout) As a result during the install of Win 10 and then upgrade of Win 11, the installer used the OEM recovery partition as the system partition. The System partition is therefore very large at nearly 8GB. As the SSD is only 128Gb I could do with removing the old Dell backup image and software. Below are images of the hard drive and each partition in order.

Can anyone recommend a safe GUI based tool that can delete files on hidden partitions and which ones are part of the active boot process I should leave alone?

1) Macrium Reflect and/or AOMEI Backupper (both freeware) to create image(s) of the existing system (so it can be restored if anything goes pear-shaped)
2) As multiple posts show in this forum, a search will reveal the GUI software of choice for partition management is Minitool Partition Wizard. Another popular one is AOMEI Partition Assistant (both freeware)
3) delete the Recovery partition, but make sure you maintain a future regular regime of system imaging

Those would appear to be the Dell Diagnostics and OEM Recovery Partitions..... What you need to figure out is if any of them or which one is the Boot Partition... Although it Might Be C:\ > which if that is the case, you can remove both those partitions..

Open Command Prompt (Admin) and type > bcdedit
see what Partition "Windows Boot manager" is on

Have you tried with Disk Management and doesn't allow you to delete it? I think you can just click to select it and then delete or right-click and select delete from the list. Then expand the Windows partition to take the available space, so restart required.

No it is not the boot partition. However, if anything happens and you cannot boot in Windows 11, use your Windows 11 USB to Repair and you are OK.