Upping rare items

[GGcannon]

Hey everyone this is my first time posting here but I've always been looking around at builds and such, but couldn't find anything on something I was thinking about recently.

I'm going to try out a double throw barb and found these rare throwing axes on one of my mules. They have about 50-220 throw damage with 20 ias, 208 enhanced dmg, and +341 attack rating. I have read in a few places about upping rare items and I think I know the formula (would be great if someone could confirm it) but what exactly will it do? Increase the damage? Reroll the mods? Keep them? I really like the ias/ed/ar so I don't want to ruin them but if there is no doubt that they will become better, I want to do it.

Thanks in advance.

[helvete]

It goes like this.

If your base item is "throwing axe", you can up to "francisca", making for higher damage, but also higher reqs.

If your base item is "francisca", you can up to "flying axe", for even higher damage, but even higher requirements.

None of the mods will be rerolled.

[GGcannon]

Ah thanks alot but it seems its already a flying axe so it can't go up anymore :(