Cisco Network Assistant (CNA) is free and provides very basic network management functionality. As a free tool it does not include any support and if the feature you want isn't already in it, it may never be added.
There's nothing I've seen called "Cisco Prime LAN". There's Cisco Prime Infrastructure (PI) and Cisco Prime LAN Management Solution (LMS), LMS is no longer sold separately although it is technically still supported.
The current primary wired and wireless network management product from Cisco is PI. It has a lot of rich features but if you're managing only two switches, the entry cost for PI may be more than the cost of the switches.
I'd start with CNA and see if it meets your needs. If so, you're done. If not, list those needs and figure out if PI (or possibly some non-Cisco product) might meet them instead.
