Assets not being removed automatically, take a look at this topic: https://www.lansweeper.com/forum/yaf_postst15929_Removing-Old-Assets---Not-working.aspx#post53649
If your switches do not have to correct asset type and are being scanned with SNMP, you can map the OID to the correct asset type by following this knowledgebase article: https://www.lansweeper.com/kb/95/changing-an-assets-asset-type.html
If you are not scanning your switches with SNMP, then I highly recommend doing so to get the most accurate information.
For scanning warranty information, I would recommend first updating to the latest Lansweeper version due to the recent warranty scanning fixes made. Then check if your assets have all the required information listed here: https://www.lansweeper.com/kb/193/scanning-warranty-information.html