As long as you have other devices using iCloud you can choose to quit syncing on your iPad and delete the photos, so they are not removed from iCloud, and that appears to be what you have already done.
When you delete the photos, they will go into the Recently Deleted folder on your device for 30 days in case you change your mind. You can free up that space before that time by removing them from the Recently Deleted folder. The steps are at the bottom of this Support Article:
Delete photos on your iPhone or iPad - Apple Support
Also make sure you do not have any in your Hidden Folder. I assume you are viewing your Photos storage by going to Settings > iPad Storage > Photos. If it shows only 293MB, there are very few if any photos taking up storage space and the amount you see includes the photos app itself. Check for other areas on the page where you can delete data.
If you are struggling to free up enough space, you can update by plugging into a computer. This way you don't need to download the update on your device first before it installs. This reduces that amount of storage space you need to update your iPad.