Frustrated While Adding Images To website

Hello everybody this is my first time here. I hope this is the right place for my questions.
End of this past January my brother recommended one of his friends to help me with my photo website. I paid him 50% upfront and now he wants the other half but I keep telling him that the site is far from done. He placed the wrong images in some of the themes and also the wrong info. I keep asking him to change it but he wants to get pay for that when in fact is part of what we agree. Then I asked him to show me how to do it so I can finish it but he will not do it since he wants me to pay him more for any changes. I do have the pass word to log in and decided to learn a few things so I can do it and stop been jerked around. I want to go live with my new photo site but not until is done well.
1. How can I ad/edit images on my site, or is there a place where I can go in to see it like a tutorial or something on you tube?
2. How can I change the size of an image that maybe too large and cuz of that is not mobile friendly since only part of the image will show.
2. How to ad a link, so you can click on Prices and it will show you all of that in another page.
IF this helps he does have a few pluggins in the site and one for photos called Photoswipe.
I am going crazy with this and really appreciate any help from anybody.

Tommy