Resize Sig Pics?

[Randi]

Here's a variation of the question

I have put some pics into Photogra and then on to PT (see Cute picture) but it's rather big. Then, I've tried to put some more pics in exactly the same way and this comes up:
UNSUPPORTED IMAGE TYPE, PLEASE SELECT A DIFFERENT IMAGE.

If I click Upload, the picture will go in anyway, but it takes a he!! of a time to do anything within the Photogra site (loading the pics takes ages) We have a fast connection, so I don't think that's the reason.

I have resized all the pics (jpeg format) to less than 150k in Photoshop first. What size should I make them? Or can I change the size in Photogra?

Can anyone help?