Try 20 mg then 30mg... uhm how?

Okay so I have a weird question (probably have to call my doctor to double check he actually meant for me to try 20 mg, then 30mg then 40mg) or not so weird but my doctor told me I can up my does of Vyvanse to see what works best.

The thing is, I have 20 mg pills so... how can I try 30 mg? In the directions it is written that I can open the pill and put the powder in like apple sauce or something.

Am I just supposed to open the pill and eyeball 50/50 of the powder or is there like a smarter solution? Bc I obviously can't use a pill cutter.

Also how do I store the other 10 mg? Thanks in advance to any answers!

Edit: Since three people asked I'll add this here, yes I am sure I heard correctly about taking a higher dose.

Before I even was eligible to try Vyvanse (unless I would have wanted to pay out of pocket for it) I had to try Focalin and Concerta first.

With Focalin I had the lowest dose possible 5mg and I was told I can up the dose up to 20mg! So I went one week with 5mg, then tried 10mg, 15mg and at the end once 20 mg but Focalin just made dead tired and nothing else.

Concerta the same thing but they only had the second lowest dose and I didn't handle the medication well at all since my heart began beating like crazy so I stopped that one pretty quickly.

Hence now we are trying Vyvanse and I was told to do the same thing again. Also 10mg Vyvanse (where I'm from it's Elvanse) does not exist, it's only 20, 30, 40, 50 mg I think?