Upgrading crankset to 48 tooth I need to change my crankset and bottom bracket, is is possible to upgrade to 48 tooth from the stock 42?
The front derailleur is shimano Alivo and has a clamp. It could be moved up to a higher position to accommodate the bigger crankset.
Will the upgrade work? Or will I have to buy a new derailleur? 



Thank you for your valuable responses, I will stick to my stock 42 tooth option. The risk of damage/danger is higher that the merits of high gearing at the top. Presently I am able to use the total gear range without any problem. I don't want to mess with the usability of the system.
What you need to do is look up the total capacity specifications of both your front and rear derailleurs.

For a front derailleur the total capacity is just the largest difference between the largest and smallest chainring tooth counts the derailleur can handle.

The total capacity is for a rear derailleur is the largest (difference between the largest and smallest chainring tooth counts) + (difference between the largest and smallest rear sprocket tooth counts) the derailleur can handle.

If the crankset with larger rings exceeds the front or rear derailleur capacities, it will not work, however, Shimano's specs are quite conservative, so you may get away with a couple of teeth over the specified max numbers.

You can look up Shimano derailleur specifications here: https://productinfo.shimano.com/#/

Another concern is chainstay clearance. Larger rings may hit the chainstays, especially as you are thinking of rings that are on the large side for a mountain bike.