Storage from Hard Drive

You should take to heart what Babowa and HWTech have said about backups. p

An excellent backup drive is this one from OWC (MacSales.com): OWC Mercury Elite Pro with USB 3.2

If your Mac is an older model that have a similar model with older connectivity. Connect OWC's Customer Support for the model that would best suit your iMac, needs and budget.

If you expect to operate from the drive then consider an external SSD model. Customer Support can direct you to what you need. I'm a satisfied customer with 6 external SSDs from OWC running all the time and one of the Mercury Elite Pros for my Time Machine.

Not sure what you are trying to do, but the "storage" on your Mac cannot be messed with, changed, or improved. Your hard drive (or SSD or whatever else it is depending on your model/year) is a piece of hardware. When it was still hard drives, it actually resembled a DVD or CD and had a laser write to it. So, although the shape and write/read times have changed, the basics have not: the space on that hard drive is and will be what you bought it with.

You can move files, photos, videos, etc. to an external drive to create more space, but you can't move the space to anything. If that is what you want to do, buy an external hard drive (safest option) to move things to. You can also move it online storage; I am not familiar with Google storage - you need to be sure that it is actually storage, not just a syncing mechanism which would mean that once you delete the file on your Mac, it is automatically deleted on iCloud.

Plus beware that Google may change the terms of use and limit the amount of storage available or even decide to stop providing the service (Google is fickle this way). Keep in mind it can take a long time to download or move data stored in the cloud. You also need to be careful with cloud storage since your data is more accessible to being accessed by people trying steal it. From time to time a cloud provider has been known to have vulnerabilities or a system misconfiguration that exposes your data stored in the cloud. You definitely want to make sure your data is encrypted and it is best if the cloud provider does not have access to the encryption keys.

Also, just because the data is in the cloud, you should not consider it as a backup. You need to make sure to have frequent & regular backups of your computer and any external media which contains important & unique data (this includes cloud storage).