[mod_IC2AdvancedMachines : Unsupported major.minor version 51.0]

Do I download JRE or JDK? (Newbie)

[ERROR STARTING SERVER Help!]

Not sure whether I fixed that error or what, but now it pops up with a new thing, ill post a picture.

[ERROR STARTING SERVER Help!]

Whenever I try to start my server by double pressing the launch.BAT file, this comes up: G:\Users\Matt\Downloads>Java -Xmx3G -Xms2G -jar Tekkit.jar nogui

Error: Unable to access jarfile Tekkit.jar

G:Users\Matt\Downloads>pause

Press any key to continue. . .

I know what the problem is, but I dont know what im meant to write in the notepad, if anybody could point out what im writing in notepad please say. :)