I have a Les Paul Junior guitar that I am learning on. This one but different color:

https://www.epiphone.com/Guitar/EPI8U8980/Les-Paul-Junior/Tobacco-Burst

The basic of basic models. The strings are out of tune further up the fret I play. The strings are newish and hold open tune pretty well. But if I check the tune further up the fret, all the strings are sharp. Using Prof. Google, it seems that I have to change the intonation of the strings. How does one go about doing it? It seems nobody needs to do it on a basic guitar because all of the videos look like they're doing it on $1000 guitars with way more screws and bolts than my guitar....

Thanks in advance!