How do I transfer my sun flowers to larger pots?

Hi,
My limit to gardening has been tomato plants in grow bags and runner beans!
This year we have planted sun flower seeds in plastic containers (Tesco trays) in our conservatory and now they are about 3 inches high with four leaves. ( starting to go a bit yellow). I want to eventually plant them out in 12 inch pots. What do I do next and what soil should I be using is tomato grow bag compost Ok ?
kairos.

 

Hello and welcome

The best way I've found to get young plants out of cells without damaging them (the plant) is this. Take a cheapo pen, and with the wrong end (ie not the pointy, writing end but the blunt end) push it into the drainage hole in the bottom of the cell. The whole thing then just pops out intact (usually). If you send the pointy end in first, all that happens is it goes straight into the compost, damaging the young roots while at the same time compressing the compost out over, so that its harder to get the young plant out.