Yosemite is now up to 10.10.1 Don't forget that update.
First after the install, Photoshop may ask for a particular brand of Java.
If so, get it here: Java for OS X 2014-001
If you are lucky CS5 will run normally. If not, you will have to reinstall it and all the updates.
CS5 is a discontinued product, there are no further updates.
Photoshop CS5 Installer is here: Download CS5 products Help > Updates should take care of the rest.
Your serial number should under the account you registered it under. Click the triangle next to Photoshop CS5 to reveal it.
Wow. Thanks so much for responding to my question! That is very kind of you and also very helpful!
I plan to do all of this during a one-to-one appt. and I am taking this info. with me, so……..
thanks, dj hall
Great if it goes well, then mark my response as the one that answered your question. It will close the case and indicate a solution to those who have the same question.