To install it on Android you just have to save your data in your account, close your account, 
uninstall the geometry dash you have and then you must download and 
install the apk you chose, load your account and go;)
To install it on PC you should download the file you leave, then unzip it by right clicking and extract here 
and the files that you can put them in your resources folder replacing them and you leave and you already have it installed;)