The fairy lights provided with your lightbox are battery powered and should last for many hours.  However, no one likes  constantly changing batteries. So, primary upgrade that I recommend is to obtain a new fairy light that is either rechargeable or one that plugs in. Both of these options can be purchased from Amazon or other sites. 

Plug-in fairy lights: (search on Amazon for "plugin fairy lights")

I recommend the USB plugin fairy lights. Using these lights will require an adapter to plug them into a wall outlet but most people have a spare USB charger available. 

A small hole can be drilled into the base of of the light box to allow a chord to be inserted. The material that the light box is made of is easily drilled with a regular wood drill bit. After drilling the small hole, feed the fairy lights through the hole until the USB plug is reached. Then wrap the fairy lights around the light frame and leave as much extra wire as needed to reach a receptacle. 

Here are a few  examples of USB fairy lights that are available on Amazon now (November, 2022);