1. When the customer is choosing size in my online store, after checking out in the cart the size is not what the customer choose, there is a technical issue, appeared the size first in the size range: for example, the order of the sizes s, m, l, if the customer choose M or L, in the cart appeared always SIZE "S"
2. Pictures published for each product, if there are more then one, when you click on them, they are not changing for customer viewing.
3. Kindly provide the email address or the contact to address these issues.
Seems there is a JS conflict in your theme that's why both of features not working for you.
To cross-check follow these steps:
1) open you store in chrome
2) Right click on page
3) Click Inspect ( last option )
4) Click on console ( Now here you can see errors. )
But if it's not a conflict then it means the theme you are using don't have these features.