Here are some thoughts which may be helpful. First, if the computer says that you need more storage to do that installation, you do. Second, where you look to see what storage you have is variable. The most reliable information will be to open Disk Utility and check it. You have three options. (1) Decide to forego any future OS upgrades. (2) Delete some pf your date to clear space. (3) Install an external disk. Copy those photos and other files to the external disk, then delete them from your hard drive to clear up needed space. Option 3 is the best. You will find that external disks are now, very compact, reasonably priced, there are many choices, and they are easy to install with a vendor provided USB cable. Most do not require any external power source. You may have to reformat it, however. That is the easiest solution.