iOS runs on the iPad and iPhone, neither of which can run Yosemite.
So back to the real story.
What computer do you have?
How old is it?
How much RAM?
What version of OS X is it currently running?
Do you see the RED note underneath your post as you are replying?
I have read comments about Yosemite in the forum section and I would like sincere advice as to wether I should do the free update from Maverick to Yosemite please? Any teething issues or not? I have IOS X, would someone be so kind and give me info on this please?