revamp shopify store, mobile app and payment channel

I’m looking for help revamping my Shopify store, Mobile app and payment channel. For the shopify store, I need a user experience improvement, but it does not need a full redesign. I do have an existing website design to work from, as well. I am looking for someone experienced in revamping such technologies to take on the task and make sure everything works efficiently.
I should mention I am located in Thailand and PayPal does not work here anymore, a workable payment channel needs to be found that actually works.