You can extract all textures of Civ V with the extract script of the SDK. I believe you will find them in the Assets folder then. Look for "City" dds. There are many textures for different cultures and eras. I can not recommend to increase their size, because you will not notice it, but feel free to try it out. If you are done with a texture, you can copy it to \Sid Meier's Civilization V\Assets\DLC\TTE_2k\Cities, if you are using my Terrain Mod. After deleting you Cache and ModUserData folder, you should be safe to see it ingame.