hey @rollandthomas,
you could easily do that by clicking the new total SP delegation amount you would like to proceed delegating. So if you had delegated before 100SP, and you would like to increase those to for example 500, just click the proper link 500 SP below.
If it's an amount that is not available, choose custom amount and enter the total amount

Delegate to Actifit 10SP, 20SP, 50SP, 100SP, 250SP, 500SP, 1000SP, 5000SP, 10000SP, 50000SP, 100000SP, Custom Amount