You can if they aren't protected, TiVo desktop will work but pytivo is better option. There currently is no option yet to backup and restore Roamio drives, if you upgrade you will be starting over unless you can copy your recordings down to the pc first.
Might install a copy of TiVo desktop first to see if the recordings can be transfered if you only have one TiVo to check the copy status since such varies from one cable company to another as this is a rescriction set by them not TiVo as it's only the TiVo that enforces what ever the cable company sets.
In case you aren't aware, there is a community 4tb upgrade option rather than the more expensive weakknees or dvrdude retail 4tb upgrade purchase.
TiVo Roamio Pro
TiVo Roamio Plus (3tb)
TiVo Mini (three)