MindonMap is great to use to upgrade your 1k textures on your old props. 
Take a look at a building from City Elements I purchased today and upgraded
the texture for the 3 buildings that are connected. 
You don't have to sign up for anything to use the free Ai Upscaler.
God Bless! and I give God all the glory for helping me.

The 4k output is about 15mb and the 2K output is about 5.5mb.

[Official] MindOnMap Free Image Upscaler Online: Easy to Use