since I downloaded new software I cannot open photos - message says I need more memory - how do I get that?

Did it say more memory or more hard drive space?

It would be unusual to say more memory. How much RAM and hard drive space do you have?

Thank you for answering.

Memory isn't the same thing as disk space (storage space). Memory is RAM and yes, the Apple store could install more. But more memory isn't what you mean.

Not enough disk space means you are filling up your drive. You could move some files to an external drive and delete them from the internal, or, you could backup your entire internal to an external drive, and then get a new larger drive installed (and copy back everything you saved).

Getting two external drives - or one large one like 2 TB size would be the cheapest route for you. ( I prefer two drives - one for backups and one for storage)

With the external storage one (or storage partition - if you divide a single drive into two parts before using it), you start moving files (music, pictures, etc) to the external and delete from the internal drive to create more space on the internal.

USB3 drives are quite cheap these days.

You need more storage space, and you need to start backing up - having each file in a second location. Time Machine (built-in on OS X) is the easiest way to backup.

Read more:

Use Time Machine to back up or restore your Mac - Apple Support

Yes, you can get one at the Apple store. But, USB3 drives are "commodities" - that is, even the cheap ones will work fine. So, I'd buy the cheapest one I could find, make sure I formatted it for OS X, then use it.