How to install saves in My Summer Car :

You need:
defaultES2file.txt (main save)
items.txt          (items save as i know)

You need to get to folger
C:\Users\<your user name>\AppData\LocalLow\Amistech\My Summer Car\
(AppData folger is hiden, so you need to turn show hiden files on)

!!!That will replace your current save!!!

Throw downloaded files into this folger with replace.