Latitude E5470 TPM Update

I seem unable to update the TPM on this laptop. I have searched for solutions, but nothing I have found seems to work. The steps I am following are as follows:

1. Suspend Bitlocker

2. Disable TPM autoprovisioning

3. Reboot laptop and enter Bios setup. Clear TPM. Disable secure boot and allow legacy ROM so I can boot from an MS-DOS USB drive. 

4. Reboot from USB drive

5. Run TPM update (DellTpm2.0_Fw1.3.2.8_V1_64.exe). It runs up to the point of "getting things ready" then just stops. I wondered if this was due to the TPM being inactivated after step 3, so I tried a reboot and activated the TPM. No difference. Also tried the /s /r and /forceit switches.

6. If I try Powershell to run the executable it complains about a driver being vunerable.

Any suggestions??

Guy