How can i get the correct pressure back in my boiler?

I have a Vaillant turbomax boiler.After having a couple of radiators removed and then put back to the wall i had to refill the heating system....However i did have problems turning the valve.When i finally got it to turn..and as i watched the pressure go into the green,between 1-1.5, i watched the needle slowly increase up into the red to 3.How do i get the pressure back into the green?..i have the installation manual,and it does look like something i could do safely,but can i..and should i do the job and if possible, can whoever talk me through the process.Should i be able to tackle this small problem on what has been an excellent boiler for me or shall i not touch it and call a professional?..Thank you