How to manage storage

A follow up question to my earlier one about the slow uploads.  (It’s now taking hours.).  I have plenty of space left on the Meural cloud for more photos but perhaps there is not enough space on the local device,  How much space is there locally?  Can I upload my photos to the Meural cloud and then just access them on the frame when I need them?  How does the interchange with the cloud work?  I have lots of linked albums.  Is this slowing up the system?