Dynamic skybox / How to update texture uniform

[avilkinnick]

Currently I have some predefined skybox files (sky_day.bmp, sky_night.bmp, sky_sunrise.bmp and so on) that, for some periods of time remain static, but for some periods (for examle, from 6:00 - 7:00) smoothly changes from one to other and it is made by only having one texture in shader, data of which is dynamically changed pixel by pixel and it is pretty slow, I want to make 2 texture uniforms and one uniform float mix value, I already solved how to update float value, but I don't understand yet how to update texture unifom so that it point to completely another image.

Source code for current implementation can be found here:
https://github.com/ArepMM/RRS/blob/v1.8.0-arepmm-dev/viewer/src/Skybox.cpp