SR4 was updated some weeks ago, and it has been recently updated. I'd strongly recommend to upgrade to this latest version (QlikView 10 SR4 build 9282). It is working fine and fixes some issues that were not fixed in SR3. So unless you have some known restrictions in hardware or software, I'd download the Release Notes and carefully do the upgrade process as described.
Yes, patch will come with the instruction of what needs to be done. Sometime they just replace some DLL files, or sometime they may ask to reinstall on top of what you have on the server. Totally depends on the patch type. You need to open a ticket with QV Support in order to get patch relevent for your issue. This pproblem I mentioned about current selection box, there is no patch built yet.
Regarding SR3-SR4 changes, please download release noted from QV download site. It will tell you what changes are there and what you need to upgrade it. Sometimes, there are special instructions, which may make your life easier with that specific upgrade.