Firstly you need to add NuGet feed for Sitecore 9.3
```
Install-Package Sitecore -Version 9.3.0 -Source https://sitecore.myget.org/F/sc-packages/api/v3/index.json
```
[![enter image description here][1]][1]

Then you need to go `Manage Nuget Package` and search DLL name then click on `update `

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/xs4hX.png
  [2]: https://i.sstatic.net/6Ru7p.png