Before upgrade ST-PI add on, you need to upgrade SPAM/SAINT tool. You can find guide here.
After this step you can follow steps below for upgrade ST-PI add-on.
Run report Se38 –> RTCCTOOL for get latest version information
Check ST-PI section for upgrade information
Check SAP Market for download 74010INSTPI.
From client 000, run transaction SPAM and load package from Front end server. Also you can copy and decompress .sar file on the OS level. You must copy files to ../trans/EPS/in folder.
Click Display/Define button for choose which add on to upgrade.
Import the queue.
Click confirm button.
You find guide for upgrade ST-A/PI here.