My Mac doesn't have enough space to do this update--requires a backup?!

[iMore Question]

When I try to install 8.1.3, I get a message saying my Mac doesn't have enough drive space to back up my iPhone 6. This seems to prevent the update to 8.1.3. Frustrating.

 

[kch50428]

Only frustrating if you want it to be that... Free up space on the Mac with an external HD, or thumb drive... Or do the update over the air on the phone.