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For this either you have to upgrade your internal hard drive by purchasing a higher capacity one or you can buy an external hard drive and store your photos on it. You can upgrade your internal hard drive up to 1TB (1024GB) or 2 TB (2048 GB). Upgrading the internal hard drive is very costly. To upgrade the internal hard drive, you have to take it to the Apple Store. It would cost more than $200 for a 2TB drive if you replace it from Apple Store. If this is a Macbook Air model, then it would cost more.
I'd recommend to buy an external hard drive. External hard drives are less costly and you can get a higher capacity one like 2TB for less than $100, which is all you need to hold your photos. When you get the external hard drive, all you have to do is connect it to your Mac's USB port and it will recognize it like a USB drive. Then you will be able to copy your photos into it.
If you have any questions or would like any additional information, please don't hesitate to ask.
You can buy the external hard drive from here --> https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=external+hard+drive+mac
This is a hardware related concern. You can't buy space from online. You will have to buy this hardware equipment (hard drive) to upgrade the space.
Also add a bookmark of this page or add this page to your favorites, so when you get the external hard drive you can get back to me directly and I will help you to save your photos to it (without paying again)
If you want, I can remotely connect to your Mac and delete some unwanted files from your Mac and free some space on your Mac now. Let me know if you would like me to do that for you.