Contact us if you you are legally in the UK and wish to change your visa category. There are few visa categories that allows you to switch into other visa categories from within the UK. for example you can switch from Tier 4 to Tier 2. If you are on any long term visa, you can switch into family visa etc.
UK visit visa can not be changed into other visa categories for example into spouse visa or work visa etc. If your current visa category does not allow you to switch, in that case, you will need to leave the UK and make an application from your home country.