I applied for UK visa and was rejected on 16th June on the grounds that I have not provided documents to verify my personal circumstances. I'm planning to reapply. My question is when completing the new application form can I change figures like my monthly income after taxes must correct what I have done wrong last time?
Yes, you can change the figures pertaining to income and financial reserves. They need to dovetail with your bank statements and salary slips. The information you provide is subject to your agreement...
That the information given on this form whether input by myself, input on my behalf by a third party or automatically pre-populated is complete and correct to the best of my knowledge and belief
...and this part...
I must inform the UK diplomatic mission if there is a material change to my circumstances, or any new information to my application becomes available.
You can find both of these terms and conditions in Part 10 of the form.
In general, the information you provide on a visa application should be an accurate representation of your current circumstances. If you submitted an application earlier this month, and your new figures are wildly different, then it's best to consult a professional.