Reduce jpg size using preview

Recently I had taken a couple of photos I wanted to use on a post but there were about the 6-7Mb size which is too big.

To reduce the size as I was on my home iMac, I opened them in Preview, selected Export then you have a slider so you can reduce the quality and therefore the size of the image

So this is easy, but I am looking for a decent way to do this on an iOS device, there seems to be plenty of apps that can do this, I am looking for a recommendation or a tip.

Please leave a comment or drop me a mail with your recommendations.

I am always interested in feedback so please feel free to add any comments, or you can mail me  here.  If you would like to submit a quick tip  with full credit and links back to your site then also feel free to contact me.