changing string gauge

Don't know the particular guitar, but it sounds as if it has a floating trem. Bends both up and down in pitch? (Also applies to some bend-down-only vintage Strat-like trems) If so, going to a higher gauge mean the tension goes up and pull the bridge forward. So yes, you have to tighten the trem spring tension to restore the bridge plate's original position. You can do this one of two ways:

1.Iteratively: Tighten the spring tension a bit, retune, check the bridge angle. If the angle is still wrong, re-adjust spring tension, retune and check again ... repeat as necessary. Note that this assumes intonation is correct. If you've changed gauges, that will need adjustment, and the nut should be checked for correct slotting/height as well.

2. Blocking the bridge (Recommended): Wedge something (wood or plastic wedges) in under the bridge plate to put it in the correct position (angle). Adjust intonation and tune. Make sure all sounds good and plays well. Note the position (angle) of the bridge plate. Now remove the blocks (wedges) and adjust the trem spring tension to return the bridge plate angle to the observed position. Tweak tuning and double check. Ready to go! This does not include nut adjustment, which can be done independently.

IF you have a bend-down only trem, simply increase the trem spring tension to pull the bridge plate back into "normal" position. And remember to check intonation, nut setup.

(last thoughts: Also will need to check neck relief (bow in neck) for string gauge change. That is a truss rod adjustment. If a noob, might want to find someone experienced to show you this, as over tightening will damage the neck. If you have really gone up a lot in gauge, nearly all of neck relief, intonation, nut setup will need tweaking. Good news: once set up correctly with a higher gauge, action can usually be set lower than with lighter gauges.)

I've changed from 9's to 11's so yeah it is a fairly steep change.

I am kind of a noob when it comes to internals & stuff.

(sorry if this sounds stupid) inside there is the bridge bit with the two springs attached to it, then another plate with two long screws (truss rods? guessing ones for treble strings ones for bass). Do i tighten the screws?

The two long screws are for tightening/loosening the spring tension, and simply are called "spring tension screws." The plate thru which they go is sometimes called the "claw," as it hooks onto one end of each spring. Turning these is fairly safe adjustment in terms of not causing damage -- you should be tighening them; that is screwing them further into the body. BTW, if you want to block the bridge, you can do it from the inside by wedging pieces between bridge plate extension at the other end of the springs -- strings are anchored in this; it's call the "inertia block."

The truss rod is in the neck, and adjustments to it (at either the headstock or base of neck where it attaches to body) change the bowing of the neck. Don't adjust the truss rod until you have advice from someone not-a-noob.

Cheers for the help. I've put my strings on & they seem fine :D

good job!