Well don't upgrade if you don't have a hackable psp with pandora battery.
You will loose your HBL if you use it.
I will provide the links but i suggest you to don't upgrade to 6.31
Main features updated in system software ver 6.31
System software stability during use of some PSP® format software titles has been improved.
Update:J416 is reporting (see here) that his exploit is indeed working on 6.31.
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