Help me please

Hello,

I 820 HTC desire and I search for firmware restore my smartphone since marshmalow blocking me on startup screen .
Info smartphone bouygues :

A51_UL PVT SHIP S- ON
H - BOOT 3.19.0.0000
RADIO 01.01.010_U10305041_08.01.51015
OS- 2.10.1020.5

Thank you to tell me or I just downloaded firmware for my phone

Thank you

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