Windows -
Btcpwallet.Fullnode.1.4.*.zip
Contained in the zip file is RunFirst.bat, double click that (it will appear to do nothing, that is ok) then run Btcpwallet.Fullnode.1.4.*.msi
If you have run previous versions of the testnet wallet and have not run RunFirst.bat you will likely have issues connecting to the new testnet.
Linux -
Btcpwallet.Fullnode.1.4.*.tar.gz
Contained in the tar.gz file is RunFirst.sh, double click that (it will appear to do nothing, that is ok) then run Btcpwallet.Fullnode.1.4.*.AppImage or install by running Btcpwallet_Fullnode_1.4.*_amd64.deb
Mac coming soon