Can i write off a new shower surround in my rental for the entire amount or does it need to be depreciate it as an asset?

There are 2 safe harbor elections you can make if you qualify, see Safe Harbor Expensing.   TurboTax will ask about these when you enter the asset.  

And if the shower qualifies for bonus depreciation, it will be offered when you enter it in the asset section.   Any of these will allow you to expense more (or all of) than regular depreciation.  

You can deduct it as a repair/maintenance.