Welcome Jason,
Firstly order "used vehicle import pack" ....
https://forms.dft.gov.uk/order-dvla-forms/
it's 8th one down the list (but that could change)
Your pack will arrive with guidance notes, and after reading these, you will understand that half the questions DO NOT APPLY TO RENAULT 4s that are more than ten years old.
Make a copy of the application form to practice on. Be careful with the original - it is carbon-sensitive.
Quite straight forward AS LONG AS YOU ARE IN POSSESSION OF THE ORIGINAL REGISTRATION DOCUMENT CLEARLY DISPLAYING DATE OF FIRST REGISTRATION. Bill of sale also handy, but not essential.
Prepare car for testing.
Raise insurance cover-note on v.i.n. (some companies will give you just 30 days before demanding U.K. index number!)
Take car for test on v.i.n.
Make copies of everything for YOUR RECORDS.
Send originals to DVLA (it's your choice to send via Royal Mail, but I always use the counter service at Swansea),
And don't forget ... best writing,
Good Luck,
N.