Hi,
First, don't upgrade to 3.0 - is old version !
2) If you want to upgrade (from J2.5 to 3.1), please wait few days, soon will be Joomla 3.2
3) To upgrade modules you need to install a new versions (for J3.1/j3.2) after migration process
4) To migrate template, also install a dedicated version for J3.x
About 3 & 4 - if you don't have programming knowledge you won't be able to upgrade your modules/template by yourself.
5) Are you sure that you need Joomal 3.x right now? maybe wait till J3.5 will be ready in next year.