Installing Android 4.1 or higher on Sony Tipo with permanently locked bootloader
Have you tried FlashTool?

This is a particular software suite for flashing ROMs on Sony handsets, however, I am not 100% confident if it supports the Tipo.

The full forum thread that discusses about this tool can be found at XDA so it might be worth a try to read the thread from beginning to end, to see if others have used it successfully on the Tipo. 

If no luck, try posting a question there on that XDA thread, identical to the above question that is asked and wait for a while for someone to answer - you do need to be patient, as people are answering in their own personal free time.

Be warned though, using this tool, you could lose data, as a result of unlocking the boot-loader, there is a FTF (Flash Tool Firmware) file available for listed and detected devices, which can circumvent this and also can re-instate the boot-loader lock mechanism.