I would say to just get a new one.
iPads are not very upgradable in that they hit a point where their operating system can no longer be updated.
This is a good time of year to get a new device due to expected holiday sales and specials.
You can probably get a new ipad for less than $500, and possibly less than $400 depending on the model
If you’re just going to surf and watch movies, you probably don’t need the power and price of an iPad Pro, an average model should work for you.
If you have an apple store near you you can go in and talk to someone there and have them give you some advice, or other electronics stores like Best Buy or Target may also have employees that can help guide you to a good model for your needs.