My Tier 4 visa expires on August 17, 7 days after my work committment is finished. I have a US passport. I will be travelling in the UK and Ireland until August 19 when I fly from Edinburgh to Geneva. How can I change my status from Tier 4 to visitor for the two days between August 17 (expiration date) and the date I leave, August 19? Is there any grace period?
Do I actually need to leave the country before expiration of my visa and return as a visitor to spend the extra two days in the UK?
There is no grace period on a Tier 4 visa (see here). Therefore, you have to leave the country and re-enter not to overstay.
As the other answer notes, you need to leave and reenter the UK in order to change your status. In fact, technically, you must leave and reenter the "Common Travel Area", which means that you can't achieve this by traveling to Ireland.
The only other option is to apply for another visa. As long as your application is being processed, you would not be overstaying. However, the visas to which you can switch from Tier 4 are unlikely to be applicable in your case. You cannot make an in-country application for a visitor visa.
In addition, you should expect to face extra scrutiny at the border when you reenter. The Home Office are especially wary of people returning soon after the end of a long term visa. Be prepared to present your itinerary and financial documents showing you have enough funds for your stay. Make sure you don't have anything essential left to do in the UK (such as returning house keys) on the off chance that you are denied entry.
