What does the Solo test involve? that will provide an idea of what you are capable of handling in flight.

In SA we have the following classes.
Solo : Can take off, land and do a basic circuit, can handle slow level flight
Bronze: as above but with figure 8 and basic landing pattern from left nd right hand bases
Silver: as above but with inside loops and roll
Gold : as above + outside loop, inverted figure 8 and high alititude spiral rudder only decent
Instructor
Display.

If your Solo means you can handle just basic flight then I would stick to the trainer for a while yet.
Ok maybe you think I'm being a bit harsh. A sport type plane or low win trainer will make it easier to do aerobatics manuevers like loops and rolls and inverted flight but it also masks bad technique and timing. A trainer will help you iron out any bad habits before you move to a more advanced plane. As you progress to bigger and more powerful planes correct technique agains becomes important. if you only want to do Sunday Sport flying then bad habits are part of the CV and you'll be fine.
If you want to advance as a RC pilot, I say keep the trainer until you can do most of the basic aerobatic moves then progress to a low wing trainer or a Stik type ARF.

The trainer is probaly hemost underated aircraft you will own and people want to move on from them ASAP simply to shed the "Trainee" stigma. Swallow the pride and stick with it till you can handle inside loops, rolls, close to stall flight, inverted flight (yes a trianer with dihedral can be flown inverted...)

I would drop a bigger engine in the engine now so that you can make some basic aerobatics more achievable with the trainer. Your trainer is also forgiving of bad technique which gives you time to analyse mistakes and correct them on the next pass.

Use it, don't use it