We have QV server deployed at one of our customers and we are about 3 to 4 releases behind the latest release. If I upgrade it to the latest what are the advantages to expect and also will upgrading it to the latest release help with some of the issues we are encountering such as downloading the report to excel?
I guess you are talking about Service Releases. It is generally very safe to move from one SR on QlikView 11.2 to the next. There is always a risk that something might break. But the 11.2 Service Releases have generally been a very steady progress towards more stability and better functionality for the browsers.
The installation will be easy with running the upgrade. Being you didn't state your hardware configuration there is one thing you need to watch out for. If you have any services Qlik services disable the upgrade will enable them.
Regarding the question about the export to excel, the release notes will give the bug fixes and what release they are in.