Login to WSA
Go to System administration --> system updates
Click Available updates
this option shows you what is upgrade options you have from your version, that is best approach of cisco recommendations always.
*** Rate All Helpful Responses ***
For WSA upgrade paths from 10.5.3 > 11.5.1, there currently are not any currently because 11.5.1 was released before 10.5.3 (both were released within 2 weeks ago). I have submitted a request to WSA Product Management have it added ASAP.
WSA - Customer Support Engineer
I discussed this with WSA developer team. The upgrade path from 10.5.3 to 11.5.1 , will be available within two weeks.
Keep an eye on the release notes as it provides upgrade paths to 11.5.1 - https://www.cisco.com/c/dam/en/us/td/docs/security/wsa/wsa11-5/WSA_11-5-x_Release_Notes.pdf
Please review the release notes for supported upgrade paths to 11.5 - https://www.cisco.com/c/dam/en/us/td/docs/security/wsa/wsa11-5/WSA_11-5-x_Release_Notes.pdf
Currently there is no upgrade path from 10.5.3 > 11.5.1