Upgrading Catalina 10.15.7 to Monterey

Trying to upgrade to Monterey. However , upgrade fails due to insufficent space. HD is approx 121GB, I only have 7GB of what I actually need other than that is just system and other. However 47GB of drive indicated as 'Other' and despite using tools can't really see where this space is being allocated . Im not hugely short of space needed for upgrade but can't save anymore and have deleted pretty much everything I can. Anyone else in same situation and advice bar going deep and trying to delete stuff Im are not sure I should ? When I use disk tools , its hard to see where the 47Gb is actually used but clearly some is related to systems. Love this work horse and don't want to ditch it over 5-10 GB for an upgrade. Even if I take off my own data 7-8GB I still can't upgrade ? TIA