i´m playing guitar with a drum software and i´m having a big dificulty in increasing and decreasing the speed of songs.
(like for example black sabbath´s snowblind)

I have no problem changing the speeds with the guitar, but the drum programing sounds "off"

Anybody has any theory to help me here?

Well, you should be changing not only the bpm but also the velocity and attack on the notes, you don't hit the drums the same way at different speeds.

is there a "math" element in the changing speed?
For example, can i change from 140bmp to 157bpm and to 123bmp
or would there are round standards like 120bmp to 140bpm to 160bmp

something like the time signature (4/4 standard)

Nah the bpm can be anything. The time signature just tells you which notes count as "beats" and how many of them there are in a measure.

At band practice my band leader is always telling the drummer to play 3bpm quicker, 5bpm slower, and so on.