Default cache folder for windows 10 and 11 is
C:\ProgramData\Jagex\RuneScape
But in case you have changed it or using an older version of Windows you can check the options by opening the game client and while it's starting up you can click the cog wheel or when it's on the login screen click RuneScape in top right corner and then options. There's a line showing where your cache folder is located and a button to open said folder (note it appears empty if you browse it using the window that opens, but there are infact files in there).
Simply delete the folder and restart the client to make it re-download your cache.
Darkness rises when silence dies.
