Welcome!

Your biggest improvement will be in the shifters and in the rear derailleur. Much of the shifting performance and feel comes from the shifters. Your bike likely has Shimano Revoshift twist shifters or lower level Altus shifters right now. The modern Alivio ones will generally work crisper and quicker, especially if you have Revoshift twist shifters. The rear derailleur is of a much different design than your current Altus derailleur -- the M4000 series uses Shimano's relatively recent "Shadow" technology which is a hand-me-down from nicer MTB groupsets. It keeps the derailleur much closer to the rear cogset for better clearance, and also uses different cable routing, so you don't have that large cable loop in the back common to Shimano derailleurs. Chain tension is also improved...it works more like a Sram derailleur than a traditional Shimano unit.

Because you're replacing the entire groupset, you probably don't have many compatibility problems to consider. The rear derailleur hanger should be the same design, and your shifters control the number of gear combinations you have. Alivio M4000 is usually 9-speed, so you'll need a 9-speed cassette and a 9-speed chain. This is probably your only potential issue -- if your bike uses a freewheel in the back, your wheel and hub will not be compatible with a 9-speed system. You'll need a wheel and hub that can accept a 9-speed cassette.