Hi Spinay70, sorry late to the thread, actually I am doing just that (upgrading Altus) - not because I have money to burn/or anything is broken but as a self-learning project (after attending a weekend bike tech course).

My boundary values are:

1. Go to 3x9 speed and stay within Altus/Acera/Alivio
2. Alivio shifters (wanted two-way release) <- the absolute worst possible reason to upgrade!

Lessons learnt:

1. This crankset range (7-speed, riveted) means that any upgrade to Alivio is major surgery: new cassette, bolted crankset etc.
2. Current incarnations of <10-speed Shimano MTB components(Altus, Acera, Alivio) are all-in on <= 40T cranksets; not hybrid friendly
3. Shimano created an off-shoot "Trekking" range for 44/48T cranksets
4. Front mechs: need to look for 63-66 degree chainstay angle FDs; most of them are for 66-69 degrees(standard for MTB frames)

Parts I chose (for upgrading to 3x9 speed)
1. Shifters: SL-M4000-L/R (two-way release - yay!!)_
2. Rear mech: RD-M4000 (wanted to see what is "Shadow" technology)
3. Front mech: FD-T4000-TS3 (this is a clamp-on; for 63-66 degrees chainstay angle)
4. Crankset: FC-T4060 (48/36/26T - notice the "T" in FC-T4060; i.e. Trekking range, not MTB range) with BB-MT800 (recommended is SM-BB52 but I had a BB-MT800 lying around)
5. My bike came with a brifter, to split off the v-brake - used some brake levers I had in the parts box
6. Cassette CS-HG400-9